[PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Ankur Arora]

This series adds clearing of contiguous page ranges for hugepages,
improving on the current page-at-a-time approach in two ways:

 - amortizes the per-page setup cost over a larger extent

 - when using string instructions, exposes the real region size
   to the processor.

A processor could use a knowledge of the extent to optimize the
clearing. AMD Zen uarchs, as an example, elide allocation of
cachelines for regions larger than L3-size.

Demand faulting a 64GB region shows performance improvements:

 $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5

                 mm/folio_zero_user    x86/folio_zero_user       change
                  (GB/s  +- %stdev)     (GB/s  +- %stdev)

   pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*

   pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
   pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy

[#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
allocation, which is higher than the maximum extent used on x86
(ARCH_CONTIG_PAGE_NR=8MB), so preempt=none|voluntary sees no improvement
with pg-sz=1GB.

Raghavendra also tested v3/v4 on AMD Genoa and sees similar improvements [1].

Changelog:

v7:
 - interface cleanups, comments for clear_user_highpages(), clear_user_pages(),
   clear_pages().
 - fixed build errors flagged by kernel test robot
 - move all x86 patches to the tail end

v6:
 - perf bench mem: update man pages and other cleanups (Namhyung Kim)
 - unify folio_zero_user() for HIGHMEM, !HIGHMEM options instead of
   working through a new config option (David Hildenbrand).
   - cleanups and simlification around that.
 (https://lore.kernel.org/lkml/20250902080816.3715913-1-ankur.a.arora@oracle.com/)

v5:
 - move the non HIGHMEM implementation of folio_zero_user() from x86
   to common code (Dave Hansen)
 - Minor naming cleanups, commit messages etc
 (https://lore.kernel.org/lkml/20250710005926.1159009-1-ankur.a.arora@oracle.com/)

v4:
 - adds perf bench workloads to exercise mmap() populate/demand-fault (Ingo)
 - inline stosb etc (PeterZ)
 - handle cooperative preemption models (Ingo)
 - interface and other cleanups all over (Ingo)
 (https://lore.kernel.org/lkml/20250616052223.723982-1-ankur.a.arora@oracle.com/)

v3:
 - get rid of preemption dependency (TIF_ALLOW_RESCHED); this version
   was limited to preempt=full|lazy.
 - override folio_zero_user() (Linus)
 (https://lore.kernel.org/lkml/20250414034607.762653-1-ankur.a.arora@oracle.com/)

v2:
 - addressed review comments from peterz, tglx.
 - Removed clear_user_pages(), and CONFIG_X86_32:clear_pages()
 - General code cleanup
 (https://lore.kernel.org/lkml/20230830184958.2333078-1-ankur.a.arora@oracle.com/)

Comments appreciated!

Also at:
  github.com/terminus/linux clear-pages.v7

[1] https://lore.kernel.org/lkml/fffd4dad-2cb9-4bc9-8a80-a70be687fd54@amd.com/

Ankur Arora (16):
  perf bench mem: Remove repetition around time measurement
  perf bench mem: Defer type munging of size to float
  perf bench mem: Move mem op parameters into a structure
  perf bench mem: Pull out init/fini logic
  perf bench mem: Switch from zalloc() to mmap()
  perf bench mem: Allow mapping of hugepages
  perf bench mem: Allow chunking on a memory region
  perf bench mem: Refactor mem_options
  perf bench mem: Add mmap() workloads
  mm: define clear_pages(), clear_user_pages()
  mm/highmem: introduce clear_user_highpages()
  arm: mm: define clear_user_highpages()
  mm: memory: support clearing page ranges
  x86/mm: Simplify clear_page_*
  x86/clear_page: Introduce clear_pages()
  x86/clear_pages: Support clearing of page-extents

 arch/arm/include/asm/page.h                  |   7 +
 arch/x86/include/asm/page_32.h               |   6 +
 arch/x86/include/asm/page_64.h               |  72 +++-
 arch/x86/lib/clear_page_64.S                 |  39 +-
 include/linux/highmem.h                      |  18 +
 include/linux/mm.h                           |  44 +++
 mm/memory.c                                  |  82 +++-
 tools/perf/Documentation/perf-bench.txt      |  58 ++-
 tools/perf/bench/bench.h                     |   1 +
 tools/perf/bench/mem-functions.c             | 390 ++++++++++++++-----
 tools/perf/bench/mem-memcpy-arch.h           |   2 +-
 tools/perf/bench/mem-memcpy-x86-64-asm-def.h |   4 +
 tools/perf/bench/mem-memset-arch.h           |   2 +-
 tools/perf/bench/mem-memset-x86-64-asm-def.h |   4 +
 tools/perf/builtin-bench.c                   |   1 +
 15 files changed, 560 insertions(+), 170 deletions(-)

-- 
2.43.5

[PATCH v7 01/16] perf bench mem: Remove repetition around time measurement

[Ankur Arora]

We have two copies of each mem benchmark: one using cycles to
measure time, the second for gettimeofday().

Unify.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c | 110 +++++++++++++------------------
 1 file changed, 46 insertions(+), 64 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 19d45c377ac1..8599ed96ee1f 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -51,6 +51,11 @@ static const struct option options[] = {
 	OPT_END()
 };
 
+union bench_clock {
+	u64		cycles;
+	struct timeval	tv;
+};
+
 typedef void *(*memcpy_t)(void *, const void *, size_t);
 typedef void *(*memset_t)(void *, int, size_t);
 
@@ -91,6 +96,26 @@ static u64 get_cycles(void)
 	return clk;
 }
 
+static void clock_get(union bench_clock *t)
+{
+	if (use_cycles)
+		t->cycles = get_cycles();
+	else
+		BUG_ON(gettimeofday(&t->tv, NULL));
+}
+
+static union bench_clock clock_diff(union bench_clock *s, union bench_clock *e)
+{
+	union bench_clock t;
+
+	if (use_cycles)
+		t.cycles = e->cycles - s->cycles;
+	else
+		timersub(&e->tv, &s->tv, &t.tv);
+
+	return t;
+}
+
 static double timeval2double(struct timeval *ts)
 {
 	return (double)ts->tv_sec + (double)ts->tv_usec / (double)USEC_PER_SEC;
@@ -109,8 +134,7 @@ static double timeval2double(struct timeval *ts)
 
 struct bench_mem_info {
 	const struct function *functions;
-	u64 (*do_cycles)(const struct function *r, size_t size, void *src, void *dst);
-	double (*do_gettimeofday)(const struct function *r, size_t size, void *src, void *dst);
+	union bench_clock (*do_op)(const struct function *r, size_t size, void *src, void *dst);
 	const char *const *usage;
 	bool alloc_src;
 };
@@ -119,7 +143,7 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 {
 	const struct function *r = &info->functions[r_idx];
 	double result_bps = 0.0;
-	u64 result_cycles = 0;
+	union bench_clock rt = { 0 };
 	void *src = NULL, *dst = zalloc(size);
 
 	printf("# function '%s' (%s)\n", r->name, r->desc);
@@ -136,25 +160,23 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 	if (bench_format == BENCH_FORMAT_DEFAULT)
 		printf("# Copying %s bytes ...\n\n", size_str);
 
-	if (use_cycles) {
-		result_cycles = info->do_cycles(r, size, src, dst);
-	} else {
-		result_bps = info->do_gettimeofday(r, size, src, dst);
-	}
+	rt = info->do_op(r, size, src, dst);
 
 	switch (bench_format) {
 	case BENCH_FORMAT_DEFAULT:
 		if (use_cycles) {
-			printf(" %14lf cycles/byte\n", (double)result_cycles/size_total);
+			printf(" %14lf cycles/byte\n", (double)rt.cycles/size_total);
 		} else {
+			result_bps = size_total/timeval2double(&rt.tv);
 			print_bps(result_bps);
 		}
 		break;
 
 	case BENCH_FORMAT_SIMPLE:
 		if (use_cycles) {
-			printf("%lf\n", (double)result_cycles/size_total);
+			printf("%lf\n", (double)rt.cycles/size_total);
 		} else {
+			result_bps = size_total/timeval2double(&rt.tv);
 			printf("%lf\n", result_bps);
 		}
 		break;
@@ -235,38 +257,21 @@ static void memcpy_prefault(memcpy_t fn, size_t size, void *src, void *dst)
 	fn(dst, src, size);
 }
 
-static u64 do_memcpy_cycles(const struct function *r, size_t size, void *src, void *dst)
+static union bench_clock do_memcpy(const struct function *r, size_t size,
+				   void *src, void *dst)
 {
-	u64 cycle_start = 0ULL, cycle_end = 0ULL;
+	union bench_clock start, end;
 	memcpy_t fn = r->fn.memcpy;
 	int i;
 
 	memcpy_prefault(fn, size, src, dst);
 
-	cycle_start = get_cycles();
+	clock_get(&start);
 	for (i = 0; i < nr_loops; ++i)
 		fn(dst, src, size);
-	cycle_end = get_cycles();
+	clock_get(&end);
 
-	return cycle_end - cycle_start;
-}
-
-static double do_memcpy_gettimeofday(const struct function *r, size_t size, void *src, void *dst)
-{
-	struct timeval tv_start, tv_end, tv_diff;
-	memcpy_t fn = r->fn.memcpy;
-	int i;
-
-	memcpy_prefault(fn, size, src, dst);
-
-	BUG_ON(gettimeofday(&tv_start, NULL));
-	for (i = 0; i < nr_loops; ++i)
-		fn(dst, src, size);
-	BUG_ON(gettimeofday(&tv_end, NULL));
-
-	timersub(&tv_end, &tv_start, &tv_diff);
-
-	return (double)(((double)size * nr_loops) / timeval2double(&tv_diff));
+	return clock_diff(&start, &end);
 }
 
 struct function memcpy_functions[] = {
@@ -292,8 +297,7 @@ int bench_mem_memcpy(int argc, const char **argv)
 {
 	struct bench_mem_info info = {
 		.functions		= memcpy_functions,
-		.do_cycles		= do_memcpy_cycles,
-		.do_gettimeofday	= do_memcpy_gettimeofday,
+		.do_op			= do_memcpy,
 		.usage			= bench_mem_memcpy_usage,
 		.alloc_src              = true,
 	};
@@ -301,9 +305,10 @@ int bench_mem_memcpy(int argc, const char **argv)
 	return bench_mem_common(argc, argv, &info);
 }
 
-static u64 do_memset_cycles(const struct function *r, size_t size, void *src __maybe_unused, void *dst)
+static union bench_clock do_memset(const struct function *r, size_t size,
+				   void *src __maybe_unused, void *dst)
 {
-	u64 cycle_start = 0ULL, cycle_end = 0ULL;
+	union bench_clock start, end;
 	memset_t fn = r->fn.memset;
 	int i;
 
@@ -313,34 +318,12 @@ static u64 do_memset_cycles(const struct function *r, size_t size, void *src __m
 	 */
 	fn(dst, -1, size);
 
-	cycle_start = get_cycles();
+	clock_get(&start);
 	for (i = 0; i < nr_loops; ++i)
 		fn(dst, i, size);
-	cycle_end = get_cycles();
+	clock_get(&end);
 
-	return cycle_end - cycle_start;
-}
-
-static double do_memset_gettimeofday(const struct function *r, size_t size, void *src __maybe_unused, void *dst)
-{
-	struct timeval tv_start, tv_end, tv_diff;
-	memset_t fn = r->fn.memset;
-	int i;
-
-	/*
-	 * We prefault the freshly allocated memory range here,
-	 * to not measure page fault overhead:
-	 */
-	fn(dst, -1, size);
-
-	BUG_ON(gettimeofday(&tv_start, NULL));
-	for (i = 0; i < nr_loops; ++i)
-		fn(dst, i, size);
-	BUG_ON(gettimeofday(&tv_end, NULL));
-
-	timersub(&tv_end, &tv_start, &tv_diff);
-
-	return (double)(((double)size * nr_loops) / timeval2double(&tv_diff));
+	return clock_diff(&start, &end);
 }
 
 static const char * const bench_mem_memset_usage[] = {
@@ -366,8 +349,7 @@ int bench_mem_memset(int argc, const char **argv)
 {
 	struct bench_mem_info info = {
 		.functions		= memset_functions,
-		.do_cycles		= do_memset_cycles,
-		.do_gettimeofday	= do_memset_gettimeofday,
+		.do_op			= do_memset,
 		.usage			= bench_mem_memset_usage,
 	};
 
-- 
2.43.5

[PATCH v7 02/16] perf bench mem: Defer type munging of size to float

[Ankur Arora]

Do type conversion to double at the point of use.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 8599ed96ee1f..fddb2acd2d3a 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -139,7 +139,7 @@ struct bench_mem_info {
 	bool alloc_src;
 };
 
-static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t size, double size_total)
+static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t size, size_t size_total)
 {
 	const struct function *r = &info->functions[r_idx];
 	double result_bps = 0.0;
@@ -165,18 +165,18 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 	switch (bench_format) {
 	case BENCH_FORMAT_DEFAULT:
 		if (use_cycles) {
-			printf(" %14lf cycles/byte\n", (double)rt.cycles/size_total);
+			printf(" %14lf cycles/byte\n", (double)rt.cycles/(double)size_total);
 		} else {
-			result_bps = size_total/timeval2double(&rt.tv);
+			result_bps = (double)size_total/timeval2double(&rt.tv);
 			print_bps(result_bps);
 		}
 		break;
 
 	case BENCH_FORMAT_SIMPLE:
 		if (use_cycles) {
-			printf("%lf\n", (double)rt.cycles/size_total);
+			printf("%lf\n", (double)rt.cycles/(double)size_total);
 		} else {
-			result_bps = size_total/timeval2double(&rt.tv);
+			result_bps = (double)size_total/timeval2double(&rt.tv);
 			printf("%lf\n", result_bps);
 		}
 		break;
@@ -199,7 +199,7 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 {
 	int i;
 	size_t size;
-	double size_total;
+	size_t size_total;
 
 	argc = parse_options(argc, argv, options, info->usage, 0);
 
@@ -212,7 +212,7 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 	}
 
 	size = (size_t)perf_atoll((char *)size_str);
-	size_total = (double)size * nr_loops;
+	size_total = size * nr_loops;
 
 	if ((s64)size <= 0) {
 		fprintf(stderr, "Invalid size:%s\n", size_str);
-- 
2.43.5

[PATCH v7 03/16] perf bench mem: Move mem op parameters into a structure

[Ankur Arora]

Move benchmark function parameters in struct bench_params.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c | 62 +++++++++++++++++---------------
 1 file changed, 34 insertions(+), 28 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index fddb2acd2d3a..4d723774c1b3 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -30,7 +30,7 @@
 
 static const char	*size_str	= "1MB";
 static const char	*function_str	= "all";
-static int		nr_loops	= 1;
+static unsigned int	nr_loops	= 1;
 static bool		use_cycles;
 static int		cycles_fd;
 
@@ -42,7 +42,7 @@ static const struct option options[] = {
 	OPT_STRING('f', "function", &function_str, "all",
 		    "Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
 
-	OPT_INTEGER('l', "nr_loops", &nr_loops,
+	OPT_UINTEGER('l', "nr_loops", &nr_loops,
 		    "Specify the number of loops to run. (default: 1)"),
 
 	OPT_BOOLEAN('c', "cycles", &use_cycles,
@@ -56,6 +56,12 @@ union bench_clock {
 	struct timeval	tv;
 };
 
+struct bench_params {
+	size_t		size;
+	size_t		size_total;
+	unsigned int	nr_loops;
+};
+
 typedef void *(*memcpy_t)(void *, const void *, size_t);
 typedef void *(*memset_t)(void *, int, size_t);
 
@@ -134,17 +140,19 @@ static double timeval2double(struct timeval *ts)
 
 struct bench_mem_info {
 	const struct function *functions;
-	union bench_clock (*do_op)(const struct function *r, size_t size, void *src, void *dst);
+	union bench_clock (*do_op)(const struct function *r, struct bench_params *p,
+				   void *src, void *dst);
 	const char *const *usage;
 	bool alloc_src;
 };
 
-static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t size, size_t size_total)
+static void __bench_mem_function(struct bench_mem_info *info, struct bench_params *p,
+				 int r_idx)
 {
 	const struct function *r = &info->functions[r_idx];
 	double result_bps = 0.0;
 	union bench_clock rt = { 0 };
-	void *src = NULL, *dst = zalloc(size);
+	void *src = NULL, *dst = zalloc(p->size);
 
 	printf("# function '%s' (%s)\n", r->name, r->desc);
 
@@ -152,7 +160,7 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 		goto out_alloc_failed;
 
 	if (info->alloc_src) {
-		src = zalloc(size);
+		src = zalloc(p->size);
 		if (src == NULL)
 			goto out_alloc_failed;
 	}
@@ -160,23 +168,23 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 	if (bench_format == BENCH_FORMAT_DEFAULT)
 		printf("# Copying %s bytes ...\n\n", size_str);
 
-	rt = info->do_op(r, size, src, dst);
+	rt = info->do_op(r, p, src, dst);
 
 	switch (bench_format) {
 	case BENCH_FORMAT_DEFAULT:
 		if (use_cycles) {
-			printf(" %14lf cycles/byte\n", (double)rt.cycles/(double)size_total);
+			printf(" %14lf cycles/byte\n", (double)rt.cycles/(double)p->size_total);
 		} else {
-			result_bps = (double)size_total/timeval2double(&rt.tv);
+			result_bps = (double)p->size_total/timeval2double(&rt.tv);
 			print_bps(result_bps);
 		}
 		break;
 
 	case BENCH_FORMAT_SIMPLE:
 		if (use_cycles) {
-			printf("%lf\n", (double)rt.cycles/(double)size_total);
+			printf("%lf\n", (double)rt.cycles/(double)p->size_total);
 		} else {
-			result_bps = (double)size_total/timeval2double(&rt.tv);
+			result_bps = (double)p->size_total/timeval2double(&rt.tv);
 			printf("%lf\n", result_bps);
 		}
 		break;
@@ -198,8 +206,7 @@ static void __bench_mem_function(struct bench_mem_info *info, int r_idx, size_t
 static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *info)
 {
 	int i;
-	size_t size;
-	size_t size_total;
+	struct bench_params p = { 0 };
 
 	argc = parse_options(argc, argv, options, info->usage, 0);
 
@@ -211,17 +218,18 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 		}
 	}
 
-	size = (size_t)perf_atoll((char *)size_str);
-	size_total = size * nr_loops;
+	p.nr_loops = nr_loops;
+	p.size = (size_t)perf_atoll((char *)size_str);
 
-	if ((s64)size <= 0) {
+	if ((s64)p.size <= 0) {
 		fprintf(stderr, "Invalid size:%s\n", size_str);
 		return 1;
 	}
+	p.size_total = p.size * p.nr_loops;
 
 	if (!strncmp(function_str, "all", 3)) {
 		for (i = 0; info->functions[i].name; i++)
-			__bench_mem_function(info, i, size, size_total);
+			__bench_mem_function(info, &p, i);
 		return 0;
 	}
 
@@ -240,7 +248,7 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 		return 1;
 	}
 
-	__bench_mem_function(info, i, size, size_total);
+	__bench_mem_function(info, &p, i);
 
 	return 0;
 }
@@ -257,18 +265,17 @@ static void memcpy_prefault(memcpy_t fn, size_t size, void *src, void *dst)
 	fn(dst, src, size);
 }
 
-static union bench_clock do_memcpy(const struct function *r, size_t size,
+static union bench_clock do_memcpy(const struct function *r, struct bench_params *p,
 				   void *src, void *dst)
 {
 	union bench_clock start, end;
 	memcpy_t fn = r->fn.memcpy;
-	int i;
 
-	memcpy_prefault(fn, size, src, dst);
+	memcpy_prefault(fn, p->size, src, dst);
 
 	clock_get(&start);
-	for (i = 0; i < nr_loops; ++i)
-		fn(dst, src, size);
+	for (unsigned int i = 0; i < p->nr_loops; ++i)
+		fn(dst, src, p->size);
 	clock_get(&end);
 
 	return clock_diff(&start, &end);
@@ -305,22 +312,21 @@ int bench_mem_memcpy(int argc, const char **argv)
 	return bench_mem_common(argc, argv, &info);
 }
 
-static union bench_clock do_memset(const struct function *r, size_t size,
+static union bench_clock do_memset(const struct function *r, struct bench_params *p,
 				   void *src __maybe_unused, void *dst)
 {
 	union bench_clock start, end;
 	memset_t fn = r->fn.memset;
-	int i;
 
 	/*
 	 * We prefault the freshly allocated memory range here,
 	 * to not measure page fault overhead:
 	 */
-	fn(dst, -1, size);
+	fn(dst, -1, p->size);
 
 	clock_get(&start);
-	for (i = 0; i < nr_loops; ++i)
-		fn(dst, i, size);
+	for (unsigned int i = 0; i < p->nr_loops; ++i)
+		fn(dst, i, p->size);
 	clock_get(&end);
 
 	return clock_diff(&start, &end);
-- 
2.43.5

[PATCH v7 04/16] perf bench mem: Pull out init/fini logic

[Ankur Arora]

No functional change.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c             | 103 +++++++++++++------
 tools/perf/bench/mem-memcpy-arch.h           |   2 +-
 tools/perf/bench/mem-memcpy-x86-64-asm-def.h |   4 +
 tools/perf/bench/mem-memset-arch.h           |   2 +-
 tools/perf/bench/mem-memset-x86-64-asm-def.h |   4 +
 5 files changed, 81 insertions(+), 34 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 4d723774c1b3..60ea20277507 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -62,15 +62,31 @@ struct bench_params {
 	unsigned int	nr_loops;
 };
 
+struct bench_mem_info {
+	const struct function *functions;
+	int (*do_op)(const struct function *r, struct bench_params *p,
+		     void *src, void *dst, union bench_clock *rt);
+	const char *const *usage;
+	bool alloc_src;
+};
+
+typedef bool (*mem_init_t)(struct bench_mem_info *, struct bench_params *,
+			   void **, void **);
+typedef void (*mem_fini_t)(struct bench_mem_info *, struct bench_params *,
+			   void **, void **);
 typedef void *(*memcpy_t)(void *, const void *, size_t);
 typedef void *(*memset_t)(void *, int, size_t);
 
 struct function {
 	const char *name;
 	const char *desc;
-	union {
-		memcpy_t memcpy;
-		memset_t memset;
+	struct {
+		mem_init_t init;
+		mem_fini_t fini;
+		union {
+			memcpy_t memcpy;
+			memset_t memset;
+		};
 	} fn;
 };
 
@@ -138,37 +154,24 @@ static double timeval2double(struct timeval *ts)
 			printf(" %14lf GB/sec\n", x / K / K / K);	\
 	} while (0)
 
-struct bench_mem_info {
-	const struct function *functions;
-	union bench_clock (*do_op)(const struct function *r, struct bench_params *p,
-				   void *src, void *dst);
-	const char *const *usage;
-	bool alloc_src;
-};
-
 static void __bench_mem_function(struct bench_mem_info *info, struct bench_params *p,
 				 int r_idx)
 {
 	const struct function *r = &info->functions[r_idx];
 	double result_bps = 0.0;
 	union bench_clock rt = { 0 };
-	void *src = NULL, *dst = zalloc(p->size);
+	void *src = NULL, *dst = NULL;
 
 	printf("# function '%s' (%s)\n", r->name, r->desc);
 
-	if (dst == NULL)
-		goto out_alloc_failed;
-
-	if (info->alloc_src) {
-		src = zalloc(p->size);
-		if (src == NULL)
-			goto out_alloc_failed;
-	}
+	if (r->fn.init && r->fn.init(info, p, &src, &dst))
+		goto out_init_failed;
 
 	if (bench_format == BENCH_FORMAT_DEFAULT)
 		printf("# Copying %s bytes ...\n\n", size_str);
 
-	rt = info->do_op(r, p, src, dst);
+	if (info->do_op(r, p, src, dst, &rt))
+		goto out_test_failed;
 
 	switch (bench_format) {
 	case BENCH_FORMAT_DEFAULT:
@@ -194,11 +197,11 @@ static void __bench_mem_function(struct bench_mem_info *info, struct bench_param
 		break;
 	}
 
+out_test_failed:
 out_free:
-	free(src);
-	free(dst);
+	if (r->fn.fini) r->fn.fini(info, p, &src, &dst);
 	return;
-out_alloc_failed:
+out_init_failed:
 	printf("# Memory allocation failed - maybe size (%s) is too large?\n", size_str);
 	goto out_free;
 }
@@ -265,8 +268,8 @@ static void memcpy_prefault(memcpy_t fn, size_t size, void *src, void *dst)
 	fn(dst, src, size);
 }
 
-static union bench_clock do_memcpy(const struct function *r, struct bench_params *p,
-				   void *src, void *dst)
+static int do_memcpy(const struct function *r, struct bench_params *p,
+		     void *src, void *dst, union bench_clock *rt)
 {
 	union bench_clock start, end;
 	memcpy_t fn = r->fn.memcpy;
@@ -278,16 +281,47 @@ static union bench_clock do_memcpy(const struct function *r, struct bench_params
 		fn(dst, src, p->size);
 	clock_get(&end);
 
-	return clock_diff(&start, &end);
+	*rt = clock_diff(&start, &end);
+
+	return 0;
+}
+
+static bool mem_alloc(struct bench_mem_info *info, struct bench_params *p,
+		      void **src, void **dst)
+{
+	bool failed;
+
+	*dst = zalloc(p->size);
+	failed = *dst == NULL;
+
+	if (info->alloc_src) {
+		*src = zalloc(p->size);
+		failed = failed || *src == NULL;
+	}
+
+	return failed;
+}
+
+static void mem_free(struct bench_mem_info *info __maybe_unused,
+		     struct bench_params *p __maybe_unused,
+		     void **src, void **dst)
+{
+	free(*dst);
+	free(*src);
+
+	*dst = *src = NULL;
 }
 
 struct function memcpy_functions[] = {
 	{ .name		= "default",
 	  .desc		= "Default memcpy() provided by glibc",
+	  .fn.init	= mem_alloc,
+	  .fn.fini	= mem_free,
 	  .fn.memcpy	= memcpy },
 
 #ifdef HAVE_ARCH_X86_64_SUPPORT
-# define MEMCPY_FN(_fn, _name, _desc) {.name = _name, .desc = _desc, .fn.memcpy = _fn},
+# define MEMCPY_FN(_fn, _init, _fini, _name, _desc)	\
+	{.name = _name, .desc = _desc, .fn.memcpy = _fn, .fn.init = _init, .fn.fini = _fini },
 # include "mem-memcpy-x86-64-asm-def.h"
 # undef MEMCPY_FN
 #endif
@@ -312,8 +346,8 @@ int bench_mem_memcpy(int argc, const char **argv)
 	return bench_mem_common(argc, argv, &info);
 }
 
-static union bench_clock do_memset(const struct function *r, struct bench_params *p,
-				   void *src __maybe_unused, void *dst)
+static int do_memset(const struct function *r, struct bench_params *p,
+		     void *src __maybe_unused, void *dst, union bench_clock *rt)
 {
 	union bench_clock start, end;
 	memset_t fn = r->fn.memset;
@@ -329,7 +363,9 @@ static union bench_clock do_memset(const struct function *r, struct bench_params
 		fn(dst, i, p->size);
 	clock_get(&end);
 
-	return clock_diff(&start, &end);
+	*rt = clock_diff(&start, &end);
+
+	return 0;
 }
 
 static const char * const bench_mem_memset_usage[] = {
@@ -340,10 +376,13 @@ static const char * const bench_mem_memset_usage[] = {
 static const struct function memset_functions[] = {
 	{ .name		= "default",
 	  .desc		= "Default memset() provided by glibc",
+	  .fn.init	= mem_alloc,
+	  .fn.fini	= mem_free,
 	  .fn.memset	= memset },
 
 #ifdef HAVE_ARCH_X86_64_SUPPORT
-# define MEMSET_FN(_fn, _name, _desc) { .name = _name, .desc = _desc, .fn.memset = _fn },
+# define MEMSET_FN(_fn, _init, _fini, _name, _desc) \
+	{.name = _name, .desc = _desc, .fn.memset = _fn, .fn.init = _init, .fn.fini = _fini },
 # include "mem-memset-x86-64-asm-def.h"
 # undef MEMSET_FN
 #endif
diff --git a/tools/perf/bench/mem-memcpy-arch.h b/tools/perf/bench/mem-memcpy-arch.h
index 5bcaec5601a8..852e48cfd8fe 100644
--- a/tools/perf/bench/mem-memcpy-arch.h
+++ b/tools/perf/bench/mem-memcpy-arch.h
@@ -2,7 +2,7 @@
 
 #ifdef HAVE_ARCH_X86_64_SUPPORT
 
-#define MEMCPY_FN(fn, name, desc)		\
+#define MEMCPY_FN(fn, init, fini, name, desc)		\
 	void *fn(void *, const void *, size_t);
 
 #include "mem-memcpy-x86-64-asm-def.h"
diff --git a/tools/perf/bench/mem-memcpy-x86-64-asm-def.h b/tools/perf/bench/mem-memcpy-x86-64-asm-def.h
index 6188e19d3129..f43038f4448b 100644
--- a/tools/perf/bench/mem-memcpy-x86-64-asm-def.h
+++ b/tools/perf/bench/mem-memcpy-x86-64-asm-def.h
@@ -1,9 +1,13 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
 MEMCPY_FN(memcpy_orig,
+	mem_alloc,
+	mem_free,
 	"x86-64-unrolled",
 	"unrolled memcpy() in arch/x86/lib/memcpy_64.S")
 
 MEMCPY_FN(__memcpy,
+	mem_alloc,
+	mem_free,
 	"x86-64-movsq",
 	"movsq-based memcpy() in arch/x86/lib/memcpy_64.S")
diff --git a/tools/perf/bench/mem-memset-arch.h b/tools/perf/bench/mem-memset-arch.h
index 53f45482663f..278c5da12d63 100644
--- a/tools/perf/bench/mem-memset-arch.h
+++ b/tools/perf/bench/mem-memset-arch.h
@@ -2,7 +2,7 @@
 
 #ifdef HAVE_ARCH_X86_64_SUPPORT
 
-#define MEMSET_FN(fn, name, desc)		\
+#define MEMSET_FN(fn, init, fini, name, desc)	\
 	void *fn(void *, int, size_t);
 
 #include "mem-memset-x86-64-asm-def.h"
diff --git a/tools/perf/bench/mem-memset-x86-64-asm-def.h b/tools/perf/bench/mem-memset-x86-64-asm-def.h
index 247c72fdfb9d..80ad1b7ea770 100644
--- a/tools/perf/bench/mem-memset-x86-64-asm-def.h
+++ b/tools/perf/bench/mem-memset-x86-64-asm-def.h
@@ -1,9 +1,13 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
 MEMSET_FN(memset_orig,
+	mem_alloc,
+	mem_free,
 	"x86-64-unrolled",
 	"unrolled memset() in arch/x86/lib/memset_64.S")
 
 MEMSET_FN(__memset,
+	mem_alloc,
+	mem_free,
 	"x86-64-stosq",
 	"movsq-based memset() in arch/x86/lib/memset_64.S")
-- 
2.43.5

[PATCH v7 05/16] perf bench mem: Switch from zalloc() to mmap()

[Ankur Arora]

Using mmap() ensures that the buffer is always aligned at a fixed
boundary. Switch to that to remove one source of variability.

Since we always want to read/write from the allocated buffers map
with pagetables pre-populated.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 60ea20277507..e97962dd8f81 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -22,9 +22,9 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/time.h>
+#include <sys/mman.h>
 #include <errno.h>
 #include <linux/time64.h>
-#include <linux/zalloc.h>
 
 #define K 1024
 
@@ -286,16 +286,33 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
 	return 0;
 }
 
+static void *bench_mmap(size_t size, bool populate)
+{
+	void *p;
+	int extra = populate ? MAP_POPULATE : 0;
+
+	p = mmap(NULL, size, PROT_READ|PROT_WRITE,
+		 extra | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+
+	return p == MAP_FAILED ? NULL : p;
+}
+
+static void bench_munmap(void *p, size_t size)
+{
+	if (p)
+		munmap(p, size);
+}
+
 static bool mem_alloc(struct bench_mem_info *info, struct bench_params *p,
 		      void **src, void **dst)
 {
 	bool failed;
 
-	*dst = zalloc(p->size);
+	*dst = bench_mmap(p->size, true);
 	failed = *dst == NULL;
 
 	if (info->alloc_src) {
-		*src = zalloc(p->size);
+		*src = bench_mmap(p->size, true);
 		failed = failed || *src == NULL;
 	}
 
@@ -306,8 +323,8 @@ static void mem_free(struct bench_mem_info *info __maybe_unused,
 		     struct bench_params *p __maybe_unused,
 		     void **src, void **dst)
 {
-	free(*dst);
-	free(*src);
+	bench_munmap(*dst, p->size);
+	bench_munmap(*src, p->size);
 
 	*dst = *src = NULL;
 }
-- 
2.43.5

[PATCH v7 06/16] perf bench mem: Allow mapping of hugepages

[Ankur Arora]

Page sizes that can be selected: 4KB, 2MB, 1GB.

Both the reservation and node from which hugepages are allocated
from are expected to be addressed by the user.

An example of page-size selection:

  $ perf bench mem memset -s 4gb -p 2mb
  # Running 'mem/memset' benchmark:
  # function 'default' (Default memset() provided by glibc)
  # Copying 4gb bytes ...

        14.919194 GB/sec
  # function 'x86-64-unrolled' (unrolled memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

        11.514503 GB/sec
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

          12.600568 GB/sec

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/Documentation/perf-bench.txt | 14 +++++++++--
 tools/perf/bench/mem-functions.c        | 33 ++++++++++++++++++++++---
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/tools/perf/Documentation/perf-bench.txt b/tools/perf/Documentation/perf-bench.txt
index 8331bd28b10e..04cdc31a0b0b 100644
--- a/tools/perf/Documentation/perf-bench.txt
+++ b/tools/perf/Documentation/perf-bench.txt
@@ -177,11 +177,16 @@ Suite for evaluating performance of simple memory copy in various ways.
 
 Options of *memcpy*
 ^^^^^^^^^^^^^^^^^^^
--l::
+-s::
 --size::
 Specify size of memory to copy (default: 1MB).
 Available units are B, KB, MB, GB and TB (case insensitive).
 
+-p::
+--page::
+Specify page-size for mapping memory buffers (default: 4KB).
+Available values are 4KB, 2MB, 1GB (case insensitive).
+
 -f::
 --function::
 Specify function to copy (default: default).
@@ -201,11 +206,16 @@ Suite for evaluating performance of simple memory set in various ways.
 
 Options of *memset*
 ^^^^^^^^^^^^^^^^^^^
--l::
+-s::
 --size::
 Specify size of memory to set (default: 1MB).
 Available units are B, KB, MB, GB and TB (case insensitive).
 
+-p::
+--page::
+Specify page-size for mapping memory buffers (default: 4KB).
+Available values are 4KB, 2MB, 1GB (case insensitive).
+
 -f::
 --function::
 Specify function to set (default: default).
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index e97962dd8f81..6aa1f02553ba 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -25,11 +25,17 @@
 #include <sys/mman.h>
 #include <errno.h>
 #include <linux/time64.h>
+#include <linux/log2.h>
 
 #define K 1024
 
+#define PAGE_SHIFT_4KB		12
+#define PAGE_SHIFT_2MB		21
+#define PAGE_SHIFT_1GB		30
+
 static const char	*size_str	= "1MB";
 static const char	*function_str	= "all";
+static const char	*page_size_str	= "4KB";
 static unsigned int	nr_loops	= 1;
 static bool		use_cycles;
 static int		cycles_fd;
@@ -39,6 +45,10 @@ static const struct option options[] = {
 		    "Specify the size of the memory buffers. "
 		    "Available units: B, KB, MB, GB and TB (case insensitive)"),
 
+	OPT_STRING('p', "page", &page_size_str, "4KB",
+		    "Specify page-size for mapping memory buffers. "
+		    "Available sizes: 4KB, 2MB, 1GB (case insensitive)"),
+
 	OPT_STRING('f', "function", &function_str, "all",
 		    "Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
 
@@ -60,6 +70,7 @@ struct bench_params {
 	size_t		size;
 	size_t		size_total;
 	unsigned int	nr_loops;
+	unsigned int	page_shift;
 };
 
 struct bench_mem_info {
@@ -202,7 +213,8 @@ static void __bench_mem_function(struct bench_mem_info *info, struct bench_param
 	if (r->fn.fini) r->fn.fini(info, p, &src, &dst);
 	return;
 out_init_failed:
-	printf("# Memory allocation failed - maybe size (%s) is too large?\n", size_str);
+	printf("# Memory allocation failed - maybe size (%s) %s?\n", size_str,
+			p->page_shift != PAGE_SHIFT_4KB ? "has insufficient hugepages" : "is too large");
 	goto out_free;
 }
 
@@ -210,6 +222,7 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 {
 	int i;
 	struct bench_params p = { 0 };
+	unsigned int page_size;
 
 	argc = parse_options(argc, argv, options, info->usage, 0);
 
@@ -230,6 +243,15 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 	}
 	p.size_total = p.size * p.nr_loops;
 
+	page_size = (unsigned int)perf_atoll((char *)page_size_str);
+	if (page_size != (1 << PAGE_SHIFT_4KB) &&
+	    page_size != (1 << PAGE_SHIFT_2MB) &&
+	    page_size != (1 << PAGE_SHIFT_1GB)) {
+		fprintf(stderr, "Invalid page-size:%s\n", page_size_str);
+		return 1;
+	}
+	p.page_shift = ilog2(page_size);
+
 	if (!strncmp(function_str, "all", 3)) {
 		for (i = 0; info->functions[i].name; i++)
 			__bench_mem_function(info, &p, i);
@@ -286,11 +308,14 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
 	return 0;
 }
 
-static void *bench_mmap(size_t size, bool populate)
+static void *bench_mmap(size_t size, bool populate, unsigned int page_shift)
 {
 	void *p;
 	int extra = populate ? MAP_POPULATE : 0;
 
+	if (page_shift != PAGE_SHIFT_4KB)
+		extra |= MAP_HUGETLB | (page_shift << MAP_HUGE_SHIFT);
+
 	p = mmap(NULL, size, PROT_READ|PROT_WRITE,
 		 extra | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
 
@@ -308,11 +333,11 @@ static bool mem_alloc(struct bench_mem_info *info, struct bench_params *p,
 {
 	bool failed;
 
-	*dst = bench_mmap(p->size, true);
+	*dst = bench_mmap(p->size, true, p->page_shift);
 	failed = *dst == NULL;
 
 	if (info->alloc_src) {
-		*src = bench_mmap(p->size, true);
+		*src = bench_mmap(p->size, true, p->page_shift);
 		failed = failed || *src == NULL;
 	}
 
-- 
2.43.5

[PATCH v7 07/16] perf bench mem: Allow chunking on a memory region

[Ankur Arora]

There can be a significant gap in memset/memcpy performance depending
on the size of the region being operated on.

With chunk-size=4kb:

  $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled

  $ perf bench mem memset -p 4kb -k 4kb -s 4gb -l 10 -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

      13.011655 GB/sec

With chunk-size=1gb:

  $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled

  $ perf bench mem memset -p 4kb -k 1gb -s 4gb -l 10 -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

      21.936355 GB/sec

So, allow the user to specify the chunk-size.

The default value is identical to the total size of the region, which
preserves current behaviour.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/Documentation/perf-bench.txt | 10 ++++++++++
 tools/perf/bench/mem-functions.c        | 20 ++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Documentation/perf-bench.txt b/tools/perf/Documentation/perf-bench.txt
index 04cdc31a0b0b..3d1455d880c3 100644
--- a/tools/perf/Documentation/perf-bench.txt
+++ b/tools/perf/Documentation/perf-bench.txt
@@ -187,6 +187,11 @@ Available units are B, KB, MB, GB and TB (case insensitive).
 Specify page-size for mapping memory buffers (default: 4KB).
 Available values are 4KB, 2MB, 1GB (case insensitive).
 
+-k::
+--chunk::
+Specify the chunk-size for each invocation. (default: 0, or full-extent)
+Available units are B, KB, MB, GB and TB (case insensitive).
+
 -f::
 --function::
 Specify function to copy (default: default).
@@ -216,6 +221,11 @@ Available units are B, KB, MB, GB and TB (case insensitive).
 Specify page-size for mapping memory buffers (default: 4KB).
 Available values are 4KB, 2MB, 1GB (case insensitive).
 
+-k::
+--chunk::
+Specify the chunk-size for each invocation. (default: 0, or full-extent)
+Available units are B, KB, MB, GB and TB (case insensitive).
+
 -f::
 --function::
 Specify function to set (default: default).
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 6aa1f02553ba..69968ba63d81 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -36,6 +36,7 @@
 static const char	*size_str	= "1MB";
 static const char	*function_str	= "all";
 static const char	*page_size_str	= "4KB";
+static const char	*chunk_size_str	= "0";
 static unsigned int	nr_loops	= 1;
 static bool		use_cycles;
 static int		cycles_fd;
@@ -49,6 +50,10 @@ static const struct option options[] = {
 		    "Specify page-size for mapping memory buffers. "
 		    "Available sizes: 4KB, 2MB, 1GB (case insensitive)"),
 
+	OPT_STRING('k', "chunk", &chunk_size_str, "0",
+		    "Specify the chunk-size for each invocation. "
+		    "Available units: B, KB, MB, GB and TB (case insensitive)"),
+
 	OPT_STRING('f', "function", &function_str, "all",
 		    "Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
 
@@ -69,6 +74,7 @@ union bench_clock {
 struct bench_params {
 	size_t		size;
 	size_t		size_total;
+	size_t		chunk_size;
 	unsigned int	nr_loops;
 	unsigned int	page_shift;
 };
@@ -243,6 +249,14 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 	}
 	p.size_total = p.size * p.nr_loops;
 
+	p.chunk_size = (size_t)perf_atoll((char *)chunk_size_str);
+	if ((s64)p.chunk_size < 0 || (s64)p.chunk_size > (s64)p.size) {
+		fprintf(stderr, "Invalid chunk_size:%s\n", chunk_size_str);
+		return 1;
+	}
+	if (!p.chunk_size)
+		p.chunk_size = p.size;
+
 	page_size = (unsigned int)perf_atoll((char *)page_size_str);
 	if (page_size != (1 << PAGE_SHIFT_4KB) &&
 	    page_size != (1 << PAGE_SHIFT_2MB) &&
@@ -300,7 +314,8 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
 
 	clock_get(&start);
 	for (unsigned int i = 0; i < p->nr_loops; ++i)
-		fn(dst, src, p->size);
+		for (size_t off = 0; off < p->size; off += p->chunk_size)
+			fn(dst + off, src + off, min(p->chunk_size, p->size - off));
 	clock_get(&end);
 
 	*rt = clock_diff(&start, &end);
@@ -402,7 +417,8 @@ static int do_memset(const struct function *r, struct bench_params *p,
 
 	clock_get(&start);
 	for (unsigned int i = 0; i < p->nr_loops; ++i)
-		fn(dst, i, p->size);
+		for (size_t off = 0; off < p->size; off += p->chunk_size)
+			fn(dst + off, i, min(p->chunk_size, p->size - off));
 	clock_get(&end);
 
 	*rt = clock_diff(&start, &end);
-- 
2.43.5

[PATCH v7 08/16] perf bench mem: Refactor mem_options

[Ankur Arora]

Split mem benchmark options into common and memset/memcpy specific.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/bench/mem-functions.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 69968ba63d81..2a23bed8c2d3 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -41,7 +41,7 @@ static unsigned int	nr_loops	= 1;
 static bool		use_cycles;
 static int		cycles_fd;
 
-static const struct option options[] = {
+static const struct option bench_common_options[] = {
 	OPT_STRING('s', "size", &size_str, "1MB",
 		    "Specify the size of the memory buffers. "
 		    "Available units: B, KB, MB, GB and TB (case insensitive)"),
@@ -50,10 +50,6 @@ static const struct option options[] = {
 		    "Specify page-size for mapping memory buffers. "
 		    "Available sizes: 4KB, 2MB, 1GB (case insensitive)"),
 
-	OPT_STRING('k', "chunk", &chunk_size_str, "0",
-		    "Specify the chunk-size for each invocation. "
-		    "Available units: B, KB, MB, GB and TB (case insensitive)"),
-
 	OPT_STRING('f', "function", &function_str, "all",
 		    "Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
 
@@ -66,6 +62,14 @@ static const struct option options[] = {
 	OPT_END()
 };
 
+static const struct option bench_mem_options[] = {
+	OPT_STRING('k', "chunk", &chunk_size_str, "0",
+		    "Specify the chunk-size for each invocation. "
+		    "Available units: B, KB, MB, GB and TB (case insensitive)"),
+	OPT_PARENT(bench_common_options),
+	OPT_END()
+};
+
 union bench_clock {
 	u64		cycles;
 	struct timeval	tv;
@@ -84,6 +88,7 @@ struct bench_mem_info {
 	int (*do_op)(const struct function *r, struct bench_params *p,
 		     void *src, void *dst, union bench_clock *rt);
 	const char *const *usage;
+	const struct option *options;
 	bool alloc_src;
 };
 
@@ -230,7 +235,7 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 	struct bench_params p = { 0 };
 	unsigned int page_size;
 
-	argc = parse_options(argc, argv, options, info->usage, 0);
+	argc = parse_options(argc, argv, info->options, info->usage, 0);
 
 	if (use_cycles) {
 		i = init_cycles();
@@ -397,6 +402,7 @@ int bench_mem_memcpy(int argc, const char **argv)
 		.functions		= memcpy_functions,
 		.do_op			= do_memcpy,
 		.usage			= bench_mem_memcpy_usage,
+		.options		= bench_mem_options,
 		.alloc_src              = true,
 	};
 
@@ -454,6 +460,7 @@ int bench_mem_memset(int argc, const char **argv)
 		.functions		= memset_functions,
 		.do_op			= do_memset,
 		.usage			= bench_mem_memset_usage,
+		.options		= bench_mem_options,
 	};
 
 	return bench_mem_common(argc, argv, &info);
-- 
2.43.5

[PATCH v7 09/16] perf bench mem: Add mmap() workloads

[Ankur Arora]

Add two mmap() workloads: one that eagerly populates a region and
another that demand faults it in.

The intent is to probe the memory subsytem performance incurred
by mmap().

  $ perf bench mem mmap -s 4gb -p 4kb -l 10 -f populate
  # Running 'mem/mmap' benchmark:
  # function 'populate' (Eagerly populated map())
  # Copying 4gb bytes ...

       1.811691 GB/sec

  $ perf bench mem mmap -s 4gb -p 2mb -l 10 -f populate
  # Running 'mem/mmap' benchmark:
  # function 'populate' (Eagerly populated mmap())
  # Copying 4gb bytes ...

      12.272017 GB/sec

  $ perf bench mem mmap -s 4gb -p 1gb -l 10 -f populate
  # Running 'mem/mmap' benchmark:
  # function 'populate' (Eagerly populated mmap())
  # Copying 4gb bytes ...

      17.085927 GB/sec

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 tools/perf/Documentation/perf-bench.txt | 34 +++++++++
 tools/perf/bench/bench.h                |  1 +
 tools/perf/bench/mem-functions.c        | 96 +++++++++++++++++++++++++
 tools/perf/builtin-bench.c              |  1 +
 4 files changed, 132 insertions(+)

diff --git a/tools/perf/Documentation/perf-bench.txt b/tools/perf/Documentation/perf-bench.txt
index 3d1455d880c3..1160224cb718 100644
--- a/tools/perf/Documentation/perf-bench.txt
+++ b/tools/perf/Documentation/perf-bench.txt
@@ -240,6 +240,40 @@ Repeat memset invocation this number of times.
 --cycles::
 Use perf's cpu-cycles event instead of gettimeofday syscall.
 
+*mmap*::
+Suite for evaluating memory subsystem performance for mmap()'d memory.
+
+Options of *mmap*
+^^^^^^^^^^^^^^^^^
+-s::
+--size::
+Specify size of memory to set (default: 1MB).
+Available units are B, KB, MB, GB and TB (case insensitive).
+
+-p::
+--page::
+Specify page-size for mapping memory buffers (default: 4KB).
+Available values are 4KB, 2MB, 1GB (case insensitive).
+
+-r::
+--randomize::
+Specify seed to randomize page access offset (default: 0, or not randomized).
+
+-f::
+--function::
+Specify function to set (default: all).
+Available functions are 'demand' and 'populate', with the first
+demand faulting pages in the region and the second using an eager
+mapping.
+
+-l::
+--nr_loops::
+Repeat mmap() invocation this number of times.
+
+-c::
+--cycles::
+Use perf's cpu-cycles event instead of gettimeofday syscall.
+
 SUITES FOR 'numa'
 ~~~~~~~~~~~~~~~~~
 *mem*::
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index 9f736423af53..8519eb5a42fa 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -28,6 +28,7 @@ int bench_syscall_fork(int argc, const char **argv);
 int bench_syscall_execve(int argc, const char **argv);
 int bench_mem_memcpy(int argc, const char **argv);
 int bench_mem_memset(int argc, const char **argv);
+int bench_mem_mmap(int argc, const char **argv);
 int bench_mem_find_bit(int argc, const char **argv);
 int bench_futex_hash(int argc, const char **argv);
 int bench_futex_wake(int argc, const char **argv);
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 2a23bed8c2d3..2908a3a796c9 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -40,6 +40,7 @@ static const char	*chunk_size_str	= "0";
 static unsigned int	nr_loops	= 1;
 static bool		use_cycles;
 static int		cycles_fd;
+static unsigned int	seed;
 
 static const struct option bench_common_options[] = {
 	OPT_STRING('s', "size", &size_str, "1MB",
@@ -81,6 +82,7 @@ struct bench_params {
 	size_t		chunk_size;
 	unsigned int	nr_loops;
 	unsigned int	page_shift;
+	unsigned int	seed;
 };
 
 struct bench_mem_info {
@@ -98,6 +100,7 @@ typedef void (*mem_fini_t)(struct bench_mem_info *, struct bench_params *,
 			   void **, void **);
 typedef void *(*memcpy_t)(void *, const void *, size_t);
 typedef void *(*memset_t)(void *, int, size_t);
+typedef void (*mmap_op_t)(void *, size_t, unsigned int, bool);
 
 struct function {
 	const char *name;
@@ -108,6 +111,7 @@ struct function {
 		union {
 			memcpy_t memcpy;
 			memset_t memset;
+			mmap_op_t mmap_op;
 		};
 	} fn;
 };
@@ -160,6 +164,14 @@ static union bench_clock clock_diff(union bench_clock *s, union bench_clock *e)
 	return t;
 }
 
+static void clock_accum(union bench_clock *a, union bench_clock *b)
+{
+	if (use_cycles)
+		a->cycles += b->cycles;
+	else
+		timeradd(&a->tv, &b->tv, &a->tv);
+}
+
 static double timeval2double(struct timeval *ts)
 {
 	return (double)ts->tv_sec + (double)ts->tv_usec / (double)USEC_PER_SEC;
@@ -271,6 +283,8 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
 	}
 	p.page_shift = ilog2(page_size);
 
+	p.seed = seed;
+
 	if (!strncmp(function_str, "all", 3)) {
 		for (i = 0; info->functions[i].name; i++)
 			__bench_mem_function(info, &p, i);
@@ -465,3 +479,85 @@ int bench_mem_memset(int argc, const char **argv)
 
 	return bench_mem_common(argc, argv, &info);
 }
+
+static void mmap_page_touch(void *dst, size_t size, unsigned int page_shift, bool random)
+{
+	unsigned long npages = size / (1 << page_shift);
+	unsigned long offset = 0, r = 0;
+
+	for (unsigned long i = 0; i < npages; i++) {
+		if (random)
+			r = rand() % (1 << page_shift);
+
+		*((char *)dst + offset + r) = *(char *)(dst + offset + r) + i;
+		offset += 1 << page_shift;
+	}
+}
+
+static int do_mmap(const struct function *r, struct bench_params *p,
+		  void *src __maybe_unused, void *dst __maybe_unused,
+		  union bench_clock *accum)
+{
+	union bench_clock start, end, diff;
+	mmap_op_t fn = r->fn.mmap_op;
+	bool populate = strcmp(r->name, "populate") == 0;
+
+	if (p->seed)
+		srand(p->seed);
+
+	for (unsigned int i = 0; i < p->nr_loops; i++) {
+		clock_get(&start);
+		dst = bench_mmap(p->size, populate, p->page_shift);
+		if (!dst)
+			goto out;
+
+		fn(dst, p->size, p->page_shift, p->seed);
+		clock_get(&end);
+		diff = clock_diff(&start, &end);
+		clock_accum(accum, &diff);
+
+		bench_munmap(dst, p->size);
+	}
+
+	return 0;
+out:
+	printf("# Memory allocation failed - maybe size (%s) %s?\n", size_str,
+			p->page_shift != PAGE_SHIFT_4KB ? "has insufficient hugepages" : "is too large");
+	return -1;
+}
+
+static const char * const bench_mem_mmap_usage[] = {
+	"perf bench mem mmap <options>",
+	NULL
+};
+
+static const struct function mmap_functions[] = {
+	{ .name		= "demand",
+	  .desc		= "Demand loaded mmap()",
+	  .fn.mmap_op	= mmap_page_touch },
+
+	{ .name		= "populate",
+	  .desc		= "Eagerly populated mmap()",
+	  .fn.mmap_op	= mmap_page_touch },
+
+	{ .name = NULL, }
+};
+
+int bench_mem_mmap(int argc, const char **argv)
+{
+	static const struct option bench_mmap_options[] = {
+		OPT_UINTEGER('r', "randomize", &seed,
+			    "Seed to randomize page access offset."),
+		OPT_PARENT(bench_common_options),
+		OPT_END()
+	};
+
+	struct bench_mem_info info = {
+		.functions		= mmap_functions,
+		.do_op			= do_mmap,
+		.usage			= bench_mem_mmap_usage,
+		.options		= bench_mmap_options,
+	};
+
+	return bench_mem_common(argc, argv, &info);
+}
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index 2c1a9f3d847a..02dea1b88228 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -65,6 +65,7 @@ static struct bench mem_benchmarks[] = {
 	{ "memcpy",	"Benchmark for memcpy() functions",		bench_mem_memcpy	},
 	{ "memset",	"Benchmark for memset() functions",		bench_mem_memset	},
 	{ "find_bit",	"Benchmark for find_bit() functions",		bench_mem_find_bit	},
+	{ "mmap",	"Benchmark for mmap() mappings",		bench_mem_mmap		},
 	{ "all",	"Run all memory access benchmarks",		NULL			},
 	{ NULL,		NULL,						NULL			}
 };
-- 
2.43.5

[PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[Ankur Arora]

Define fallback versions of clear_pages(), clear_user_pages().

In absence of architectural primitives, we just clear pages
sequentially.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1ae97a0b8ec7..0cde9b01da5e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order) {}
 #endif	/* CONFIG_DEBUG_PAGEALLOC */
 
+#ifndef clear_pages
+/**
+ * clear_pages() - clear a page range using a kernel virtual address.
+ * @addr: start address
+ * @npages: number of pages
+ *
+ * Assumes that (@addr, +@npages) references a kernel region.
+ * Does absolutely no exception handling.
+ */
+static inline void clear_pages(void *addr, unsigned int npages)
+{
+	do {
+		clear_page(addr);
+		addr += PAGE_SIZE;
+	} while (--npages);
+}
+#endif
+
+#ifndef clear_user_pages
+/**
+ * clear_user_pages() - clear a page range mapped by the user.
+ * @addr: kernel mapped address
+ * @vaddr: user mapped address
+ * @pg: start page
+ * @npages: number of pages
+ *
+ * Assumes that the region (@addr, +@npages) has been validated
+ * already so this does no exception handling.
+ */
+#define clear_user_pages(addr, vaddr, pg, npages)	\
+do {							\
+	clear_user_page(addr, vaddr, pg);		\
+	addr += PAGE_SIZE;				\
+	vaddr += PAGE_SIZE;				\
+	pg++;						\
+} while (--npages)
+#endif
+
 #ifdef __HAVE_ARCH_GATE_AREA
 extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
 extern int in_gate_area_no_mm(unsigned long addr);
-- 
2.43.5

[PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[Ankur Arora]

Define clear_user_highpages() which clears pages sequentially using
the single page variant.

With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
primitive clear_user_pages().

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 include/linux/highmem.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 6234f316468c..ed609987e24d 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 }
 #endif
 
+#ifndef clear_user_highpages
+static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
+					unsigned int npages)
+{
+	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
+		void *base = page_address(page);
+		clear_user_pages(base, vaddr, page, npages);
+		return;
+	}
+
+	do {
+		clear_user_highpage(page, vaddr);
+		vaddr += PAGE_SIZE;
+		page++;
+	} while (--npages);
+}
+#endif
+
 #ifndef vma_alloc_zeroed_movable_folio
 /**
  * vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.
-- 
2.43.5

[PATCH v7 12/16] arm: mm: define clear_user_highpages()

[Ankur Arora]

For configurations with CONFIG_MMU we do not define clear_user_page().
This runs into issues for configurations with !CONFIG_HIGHMEM, because
clear_user_highpages() expects to clear_user_page() (via a default
version of clear_user_pages()).

Define clear_user_highpages() so it can supercede the generic version.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509030341.jBuh7Fma-lkp@intel.com/
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/arm/include/asm/page.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
index ef11b721230e..ddcc8159b075 100644
--- a/arch/arm/include/asm/page.h
+++ b/arch/arm/include/asm/page.h
@@ -151,6 +151,13 @@ extern void __cpu_copy_user_highpage(struct page *to, struct page *from,
 #define clear_user_highpage(page,vaddr)		\
 	 __cpu_clear_user_highpage(page, vaddr)
 
+#define clear_user_highpages(page, vaddr, npages)	\
+do {							\
+	clear_user_highpage(page, vaddr);		\
+	vaddr += PAGE_SIZE;				\
+	page++;						\
+} while (--npages)
+
 #define __HAVE_ARCH_COPY_USER_HIGHPAGE
 #define copy_user_highpage(to,from,vaddr,vma)	\
 	__cpu_copy_user_highpage(to, from, vaddr, vma)
-- 
2.43.5

[PATCH v7 13/16] mm: memory: support clearing page ranges

[Ankur Arora]

Change folio_zero_user() to clear contiguous page ranges instead of
clearing using the current page-at-a-time approach. Exposing the largest
feasible length can be useful in enabling processors to optimize based
on extent.

However, clearing in large chunks can have two problems:

 - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
   (larger folios don't have any expectation of cache locality).

 - preemption latency when clearing large folios.

Handle the first by splitting the clearing in three parts: the
faulting page and its immediate locality, its left and right
regions; with the local neighbourhood cleared last.

The second problem becomes relevant when running under cooperative
preemption models. Limit the worst case preemption latency by clearing
in architecture specified PAGE_CONTIG_NR units, using a default value
of 1 where not specified.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 include/linux/mm.h |  6 ++++
 mm/memory.c        | 82 ++++++++++++++++++++++++++++++++++------------
 2 files changed, 67 insertions(+), 21 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0cde9b01da5e..29b2a8bf7b4f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3768,6 +3768,12 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order) {}
 #endif	/* CONFIG_DEBUG_PAGEALLOC */
 
+#ifndef ARCH_PAGE_CONTIG_NR
+#define PAGE_CONTIG_NR	1
+#else
+#define PAGE_CONTIG_NR	ARCH_PAGE_CONTIG_NR
+#endif
+
 #ifndef clear_pages
 /**
  * clear_pages() - clear a page range using a kernel virtual address.
diff --git a/mm/memory.c b/mm/memory.c
index 0ba4f6b71847..0f5b1900b480 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7021,40 +7021,80 @@ static inline int process_huge_page(
 	return 0;
 }
 
-static void clear_gigantic_page(struct folio *folio, unsigned long addr_hint,
-				unsigned int nr_pages)
+/*
+ * Clear contiguous pages chunking them up when running under
+ * non-preemptible models.
+ */
+static void clear_contig_highpages(struct page *page, unsigned long addr,
+				   unsigned int npages)
 {
-	unsigned long addr = ALIGN_DOWN(addr_hint, folio_size(folio));
-	int i;
+	unsigned int i, count, unit;
 
-	might_sleep();
-	for (i = 0; i < nr_pages; i++) {
+	unit = preempt_model_preemptible() ? npages : PAGE_CONTIG_NR;
+
+	for (i = 0; i < npages; ) {
+		count = min(unit, npages - i);
+		clear_user_highpages(nth_page(page, i),
+				     addr + i * PAGE_SIZE, count);
+		i += count;
 		cond_resched();
-		clear_user_highpage(folio_page(folio, i), addr + i * PAGE_SIZE);
 	}
 }
 
-static int clear_subpage(unsigned long addr, int idx, void *arg)
-{
-	struct folio *folio = arg;
-
-	clear_user_highpage(folio_page(folio, idx), addr);
-	return 0;
-}
-
 /**
  * folio_zero_user - Zero a folio which will be mapped to userspace.
  * @folio: The folio to zero.
- * @addr_hint: The address will be accessed or the base address if uncelar.
+ * @addr_hint: The address accessed by the user or the base address.
+ *
+ * Uses architectural support for clear_pages() to zero page extents
+ * instead of clearing page-at-a-time.
+ *
+ * Clearing of small folios (< MAX_ORDER_NR_PAGES) is split in three parts:
+ * pages in the immediate locality of the faulting page, and its left, right
+ * regions; the local neighbourhood cleared last in order to keep cache
+ * lines of the target region hot.
+ *
+ * For larger folios we assume that there is no expectation of cache locality
+ * and just do a straight zero.
  */
 void folio_zero_user(struct folio *folio, unsigned long addr_hint)
 {
-	unsigned int nr_pages = folio_nr_pages(folio);
+	unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio));
+	const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE;
+	const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);
+	const int width = 2; /* number of pages cleared last on either side */
+	struct range r[3];
+	int i;
 
-	if (unlikely(nr_pages > MAX_ORDER_NR_PAGES))
-		clear_gigantic_page(folio, addr_hint, nr_pages);
-	else
-		process_huge_page(addr_hint, nr_pages, clear_subpage, folio);
+	if (folio_nr_pages(folio) > MAX_ORDER_NR_PAGES) {
+		clear_contig_highpages(folio_page(folio, 0),
+					base_addr, folio_nr_pages(folio));
+		return;
+	}
+
+	/*
+	 * Faulting page and its immediate neighbourhood. Cleared at the end to
+	 * ensure it sticks around in the cache.
+	 */
+	r[2] = DEFINE_RANGE(clamp_t(s64, fault_idx - width, pg.start, pg.end),
+			    clamp_t(s64, fault_idx + width, pg.start, pg.end));
+
+	/* Region to the left of the fault */
+	r[1] = DEFINE_RANGE(pg.start,
+			    clamp_t(s64, r[2].start-1, pg.start-1, r[2].start));
+
+	/* Region to the right of the fault: always valid for the common fault_idx=0 case. */
+	r[0] = DEFINE_RANGE(clamp_t(s64, r[2].end+1, r[2].end, pg.end+1),
+			    pg.end);
+
+	for (i = 0; i <= 2; i++) {
+		unsigned int npages = range_len(&r[i]);
+		struct page *page = folio_page(folio, r[i].start);
+		unsigned long addr = base_addr + folio_page_idx(folio, page) * PAGE_SIZE;
+
+		if (npages > 0)
+			clear_contig_highpages(page, addr, npages);
+	}
 }
 
 static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
-- 
2.43.5

[PATCH v7 14/16] x86/mm: Simplify clear_page_*

[Ankur Arora]

clear_page_rep() and clear_page_erms() are wrappers around "REP; STOS"
variations. Inlining gets rid of an unnecessary CALL/RET (which isn't
free when using RETHUNK speculative execution mitigations.)
Fixup and rename clear_page_orig() to adapt to the changed calling
convention.

Also add a comment from Dave Hansen detailing various clearing mechanisms
used in clear_page().

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/x86/include/asm/page_32.h |  6 +++++
 arch/x86/include/asm/page_64.h | 42 ++++++++++++++++++++++++++--------
 arch/x86/lib/clear_page_64.S   | 39 +++++++------------------------
 3 files changed, 46 insertions(+), 41 deletions(-)

diff --git a/arch/x86/include/asm/page_32.h b/arch/x86/include/asm/page_32.h
index 0c623706cb7e..19fddb002cc9 100644
--- a/arch/x86/include/asm/page_32.h
+++ b/arch/x86/include/asm/page_32.h
@@ -17,6 +17,12 @@ extern unsigned long __phys_addr(unsigned long);
 
 #include <linux/string.h>
 
+/**
+ * clear_page() - clear a page using a kernel virtual address.
+ * @page: address of kernel page
+ *
+ * Does absolutely no exception handling.
+ */
 static inline void clear_page(void *page)
 {
 	memset(page, 0, PAGE_SIZE);
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 015d23f3e01f..17b6ae89e211 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -40,23 +40,45 @@ extern unsigned long __phys_addr_symbol(unsigned long);
 
 #define __phys_reloc_hide(x)	(x)
 
-void clear_page_orig(void *page);
-void clear_page_rep(void *page);
-void clear_page_erms(void *page);
+void memzero_page_aligned_unrolled(void *addr, u64 len);
 
+/**
+ * clear_page() - clear a page using a kernel virtual address.
+ * @page: address of kernel page
+ *
+ * Switch between three implementations of page clearing based on CPU
+ * capabilities:
+ *
+ *  - memzero_page_aligned_unrolled(): the oldest, slowest and universally
+ *    supported method. Zeroes via 8-byte MOV instructions unrolled 8x
+ *    to write a 64-byte cacheline in each loop iteration..
+ *
+ *  - "rep stosq": really old CPUs had crummy REP implementations.
+ *    Vendor CPU setup code sets 'REP_GOOD' on CPUs where REP can be
+ *    trusted. The instruction writes 8-byte per REP iteration but
+ *    CPUs can internally batch these together and do larger writes.
+ *
+ *  - "rep stosb": CPUs that enumerate 'ERMS' have an improved STOS
+ *    implementation that is less picky about alignment and where
+ *    STOSB (1-byte at a time) is actually faster than STOSQ (8-bytes
+ *    at a time.)
+ *
+ * Does absolutely no exception handling.
+ */
 static inline void clear_page(void *page)
 {
+	u64 len = PAGE_SIZE;
 	/*
 	 * Clean up KMSAN metadata for the page being cleared. The assembly call
 	 * below clobbers @page, so we perform unpoisoning before it.
 	 */
-	kmsan_unpoison_memory(page, PAGE_SIZE);
-	alternative_call_2(clear_page_orig,
-			   clear_page_rep, X86_FEATURE_REP_GOOD,
-			   clear_page_erms, X86_FEATURE_ERMS,
-			   "=D" (page),
-			   "D" (page),
-			   "cc", "memory", "rax", "rcx");
+	kmsan_unpoison_memory(page, len);
+	asm volatile(ALTERNATIVE_2("call memzero_page_aligned_unrolled",
+				   "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
+				   "rep stosb", X86_FEATURE_ERMS)
+			: "+c" (len), "+D" (page), ASM_CALL_CONSTRAINT
+			: "a" (0)
+			: "cc", "memory");
 }
 
 void copy_page(void *to, void *from);
diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index a508e4a8c66a..27debe0c018c 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -6,30 +6,15 @@
 #include <asm/asm.h>
 
 /*
- * Most CPUs support enhanced REP MOVSB/STOSB instructions. It is
- * recommended to use this when possible and we do use them by default.
- * If enhanced REP MOVSB/STOSB is not available, try to use fast string.
- * Otherwise, use original.
+ * Zero page aligned region.
+ * %rdi	- dest
+ * %rcx	- length
  */
-
-/*
- * Zero a page.
- * %rdi	- page
- */
-SYM_TYPED_FUNC_START(clear_page_rep)
-	movl $4096/8,%ecx
-	xorl %eax,%eax
-	rep stosq
-	RET
-SYM_FUNC_END(clear_page_rep)
-EXPORT_SYMBOL_GPL(clear_page_rep)
-
-SYM_TYPED_FUNC_START(clear_page_orig)
-	xorl   %eax,%eax
-	movl   $4096/64,%ecx
+SYM_TYPED_FUNC_START(memzero_page_aligned_unrolled)
+	shrq   $6, %rcx
 	.p2align 4
 .Lloop:
-	decl	%ecx
+	decq	%rcx
 #define PUT(x) movq %rax,x*8(%rdi)
 	movq %rax,(%rdi)
 	PUT(1)
@@ -43,16 +28,8 @@ SYM_TYPED_FUNC_START(clear_page_orig)
 	jnz	.Lloop
 	nop
 	RET
-SYM_FUNC_END(clear_page_orig)
-EXPORT_SYMBOL_GPL(clear_page_orig)
-
-SYM_TYPED_FUNC_START(clear_page_erms)
-	movl $4096,%ecx
-	xorl %eax,%eax
-	rep stosb
-	RET
-SYM_FUNC_END(clear_page_erms)
-EXPORT_SYMBOL_GPL(clear_page_erms)
+SYM_FUNC_END(memzero_page_aligned_unrolled)
+EXPORT_SYMBOL_GPL(memzero_page_aligned_unrolled)
 
 /*
  * Default clear user-space.
-- 
2.43.5

[PATCH v7 15/16] x86/clear_page: Introduce clear_pages()

[Ankur Arora]

Performance when clearing with string instructions (x86-64-stosq and
similar) can vary significantly based on the chunk-size used.

  $ perf bench mem memset -k 4KB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      13.748208 GB/sec

  $ perf bench mem memset -k 2MB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in
  # arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      15.067900 GB/sec

  $ perf bench mem memset -k 1GB -s 4GB -f x86-64-stosq
  # Running 'mem/memset' benchmark:
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4GB bytes ...

      38.104311 GB/sec

(Both on AMD Milan.)

With a change in chunk-size of 4KB to 1GB, we see the performance go
from 13.7 GB/sec to 38.1 GB/sec. For a chunk-size of 2MB the change isn't
quite as drastic but it is worth adding a clear_page() variant that can
handle contiguous page-extents.

Define clear_user_pages() while at it.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/x86/include/asm/page_64.h | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 17b6ae89e211..289b31a4c910 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -43,8 +43,11 @@ extern unsigned long __phys_addr_symbol(unsigned long);
 void memzero_page_aligned_unrolled(void *addr, u64 len);
 
 /**
- * clear_page() - clear a page using a kernel virtual address.
- * @page: address of kernel page
+ * clear_page() - clear a page range using a kernel virtual address.
+ * @addr: start address
+ * @npages: number of pages
+ *
+ * Assumes that (@addr, +@npages) references a kernel region.
  *
  * Switch between three implementations of page clearing based on CPU
  * capabilities:
@@ -65,21 +68,35 @@ void memzero_page_aligned_unrolled(void *addr, u64 len);
  *
  * Does absolutely no exception handling.
  */
-static inline void clear_page(void *page)
+static inline void clear_pages(void *addr, unsigned int npages)
 {
-	u64 len = PAGE_SIZE;
+	u64 len = npages * PAGE_SIZE;
 	/*
-	 * Clean up KMSAN metadata for the page being cleared. The assembly call
-	 * below clobbers @page, so we perform unpoisoning before it.
+	 * Clean up KMSAN metadata for the pages being cleared. The assembly call
+	 * below clobbers @addr, so we perform unpoisoning before it.
 	 */
-	kmsan_unpoison_memory(page, len);
+	kmsan_unpoison_memory(addr, len);
 	asm volatile(ALTERNATIVE_2("call memzero_page_aligned_unrolled",
 				   "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
 				   "rep stosb", X86_FEATURE_ERMS)
-			: "+c" (len), "+D" (page), ASM_CALL_CONSTRAINT
+			: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
 			: "a" (0)
 			: "cc", "memory");
 }
+#define clear_pages clear_pages
+
+struct page;
+static inline void clear_user_pages(void *page, unsigned long vaddr,
+				    struct page *pg, unsigned int npages)
+{
+	clear_pages(page, npages);
+}
+#define clear_user_pages clear_user_pages
+
+static inline void clear_page(void *addr)
+{
+	clear_pages(addr, 1);
+}
 
 void copy_page(void *to, void *from);
 KCFI_REFERENCE(copy_page);
-- 
2.43.5

[PATCH v7 16/16] x86/clear_pages: Support clearing of page-extents

[Ankur Arora]

Define ARCH_PAGE_CONTIG_NR which is used by folio_zero_user() to
decide the maximum contiguous page range to be zeroed when running
under cooperative preemption models. This allows the processor --
when using string instructions (REP; STOS) -- to optimize based on
the size of the region.

The resultant performance depends on the kinds of optimizations
available to the microarch for the region being cleared. Two classes
of optimizations:

  - clearing iteration costs can be amortized over a range larger
    than a single page.
  - cacheline allocation elision (seen on AMD Zen models).

Testing a demand fault workload shows an improved baseline from the
first optimization and a larger improvement when the region being
cleared is large enough for the second optimization.

AMD Milan (EPYC 7J13, boost=0, region=64GB on the local NUMA node):

 $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5

                 mm/folio_zero_user    x86/folio_zero_user       change
                  (GB/s  +- %stdev)     (GB/s  +- %stdev)

   pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*

   pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
   pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy

[#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
allocation, which is larger than ARCH_PAGE_CONTIG_NR, so
preempt=none|voluntary see no improvement on the pg-sz=1GB.

The improvement due to the CPU eliding cacheline allocation for
pg-sz=1GB can be seen in the reduced L1-dcache-loads:

   - 44,513,459,667      cycles                           #    2.420 GHz                         ( +-  0.44% )  (35.71%)
   -  1,378,032,592      instructions                     #    0.03  insn per cycle
   - 11,224,288,082      L1-dcache-loads                  #  610.187 M/sec                       ( +-  0.08% )  (35.72%)
   -  5,373,473,118      L1-dcache-load-misses            #   47.87% of all L1-dcache accesses   ( +-  0.00% )  (35.71%)

   + 20,093,219,076      cycles                           #    2.421 GHz                         ( +-  3.64% )  (35.69%)
   +  1,378,032,592      instructions                     #    0.03  insn per cycle
   +    186,525,095      L1-dcache-loads                  #   22.479 M/sec                       ( +-  2.11% )  (35.74%)
   +     73,479,687      L1-dcache-load-misses            #   39.39% of all L1-dcache accesses   ( +-  3.03% )  (35.74%)

Also as mentioned earlier, the baseline improvement is not specific to
AMD Zen*. Intel Icelakex (pg-sz=2MB|1GB) sees a similar improvement as
the Milan pg-sz=2MB workload above (~35%).

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/x86/include/asm/page_64.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 289b31a4c910..2361066d175e 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -40,6 +40,13 @@ extern unsigned long __phys_addr_symbol(unsigned long);
 
 #define __phys_reloc_hide(x)	(x)
 
+/*
+ * When running under voluntary preemption models, limit the max extent
+ * being cleared to pages worth 8MB. With a clearing BW of ~10GBps, this
+ * should result in worst case scheduling latency of ~1ms.
+ */
+#define ARCH_PAGE_CONTIG_NR (8 << (20 - PAGE_SHIFT))
+
 void memzero_page_aligned_unrolled(void *addr, u64 len);
 
 /**
-- 
2.43.5

Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Arnaldo Carvalho de Melo]

On Wed, Sep 17, 2025 at 08:24:02AM -0700, Ankur Arora wrote:
> This series adds clearing of contiguous page ranges for hugepages,
> improving on the current page-at-a-time approach in two ways:
> 
>  - amortizes the per-page setup cost over a larger extent
> 
>  - when using string instructions, exposes the real region size
>    to the processor.
> 
> A processor could use a knowledge of the extent to optimize the
> clearing. AMD Zen uarchs, as an example, elide allocation of
> cachelines for regions larger than L3-size.
> 
> Demand faulting a 64GB region shows performance improvements:
> 
>  $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5
> 
>                  mm/folio_zero_user    x86/folio_zero_user       change
>                   (GB/s  +- %stdev)     (GB/s  +- %stdev)
> 
>    pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*
> 
>    pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
>    pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy
> 
> [#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
> allocation, which is higher than the maximum extent used on x86
> (ARCH_CONTIG_PAGE_NR=8MB), so preempt=none|voluntary sees no improvement
> with pg-sz=1GB.

I'm picking up the tools/perf part for perf-tools-next (v6.18), already
almost 100% reviewed by Namhyung.

Thanks,

- Arnaldo
 
> Raghavendra also tested v3/v4 on AMD Genoa and sees similar improvements [1].
> 
> Changelog:
> 
> v7:
>  - interface cleanups, comments for clear_user_highpages(), clear_user_pages(),
>    clear_pages().
>  - fixed build errors flagged by kernel test robot
>  - move all x86 patches to the tail end
> 
> v6:
>  - perf bench mem: update man pages and other cleanups (Namhyung Kim)
>  - unify folio_zero_user() for HIGHMEM, !HIGHMEM options instead of
>    working through a new config option (David Hildenbrand).
>    - cleanups and simlification around that.
>  (https://lore.kernel.org/lkml/20250902080816.3715913-1-ankur.a.arora@oracle.com/)
> 
> v5:
>  - move the non HIGHMEM implementation of folio_zero_user() from x86
>    to common code (Dave Hansen)
>  - Minor naming cleanups, commit messages etc
>  (https://lore.kernel.org/lkml/20250710005926.1159009-1-ankur.a.arora@oracle.com/)
> 
> v4:
>  - adds perf bench workloads to exercise mmap() populate/demand-fault (Ingo)
>  - inline stosb etc (PeterZ)
>  - handle cooperative preemption models (Ingo)
>  - interface and other cleanups all over (Ingo)
>  (https://lore.kernel.org/lkml/20250616052223.723982-1-ankur.a.arora@oracle.com/)
> 
> v3:
>  - get rid of preemption dependency (TIF_ALLOW_RESCHED); this version
>    was limited to preempt=full|lazy.
>  - override folio_zero_user() (Linus)
>  (https://lore.kernel.org/lkml/20250414034607.762653-1-ankur.a.arora@oracle.com/)
> 
> v2:
>  - addressed review comments from peterz, tglx.
>  - Removed clear_user_pages(), and CONFIG_X86_32:clear_pages()
>  - General code cleanup
>  (https://lore.kernel.org/lkml/20230830184958.2333078-1-ankur.a.arora@oracle.com/)
> 
> Comments appreciated!
> 
> Also at:
>   github.com/terminus/linux clear-pages.v7
> 
> [1] https://lore.kernel.org/lkml/fffd4dad-2cb9-4bc9-8a80-a70be687fd54@amd.com/
> 
> Ankur Arora (16):
>   perf bench mem: Remove repetition around time measurement
>   perf bench mem: Defer type munging of size to float
>   perf bench mem: Move mem op parameters into a structure
>   perf bench mem: Pull out init/fini logic
>   perf bench mem: Switch from zalloc() to mmap()
>   perf bench mem: Allow mapping of hugepages
>   perf bench mem: Allow chunking on a memory region
>   perf bench mem: Refactor mem_options
>   perf bench mem: Add mmap() workloads
>   mm: define clear_pages(), clear_user_pages()
>   mm/highmem: introduce clear_user_highpages()
>   arm: mm: define clear_user_highpages()
>   mm: memory: support clearing page ranges
>   x86/mm: Simplify clear_page_*
>   x86/clear_page: Introduce clear_pages()
>   x86/clear_pages: Support clearing of page-extents
> 
>  arch/arm/include/asm/page.h                  |   7 +
>  arch/x86/include/asm/page_32.h               |   6 +
>  arch/x86/include/asm/page_64.h               |  72 +++-
>  arch/x86/lib/clear_page_64.S                 |  39 +-
>  include/linux/highmem.h                      |  18 +
>  include/linux/mm.h                           |  44 +++
>  mm/memory.c                                  |  82 +++-
>  tools/perf/Documentation/perf-bench.txt      |  58 ++-
>  tools/perf/bench/bench.h                     |   1 +
>  tools/perf/bench/mem-functions.c             | 390 ++++++++++++++-----
>  tools/perf/bench/mem-memcpy-arch.h           |   2 +-
>  tools/perf/bench/mem-memcpy-x86-64-asm-def.h |   4 +
>  tools/perf/bench/mem-memset-arch.h           |   2 +-
>  tools/perf/bench/mem-memset-x86-64-asm-def.h |   4 +
>  tools/perf/builtin-bench.c                   |   1 +
>  15 files changed, 560 insertions(+), 170 deletions(-)
> 
> -- 
> 2.43.5

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[Andrew Morton]

On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora <ankur.a.arora@oracle.com> wrote:

> Change folio_zero_user() to clear contiguous page ranges instead of
> clearing using the current page-at-a-time approach. Exposing the largest
> feasible length can be useful in enabling processors to optimize based
> on extent.

This patch is something which MM developers might care to take a closer
look at.

> However, clearing in large chunks can have two problems:
> 
>  - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>    (larger folios don't have any expectation of cache locality).
> 
>  - preemption latency when clearing large folios.
> 
> Handle the first by splitting the clearing in three parts: the
> faulting page and its immediate locality, its left and right
> regions; with the local neighbourhood cleared last.

Has this optimization been shown to be beneficial?

If so, are you able to share some measurements?

If not, maybe it should be removed?

> ...
>
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -7021,40 +7021,80 @@ static inline int process_huge_page(
>  	return 0;
>  }
>  
> -static void clear_gigantic_page(struct folio *folio, unsigned long addr_hint,
> -				unsigned int nr_pages)
> +/*
> + * Clear contiguous pages chunking them up when running under
> + * non-preemptible models.
> + */
> +static void clear_contig_highpages(struct page *page, unsigned long addr,
> +				   unsigned int npages)

Called "_highpages" because it wraps clear_user_highpages().  It really
should be called clear_contig_user_highpages() ;)  (Not serious)

>  {
> -	unsigned long addr = ALIGN_DOWN(addr_hint, folio_size(folio));
> -	int i;
> +	unsigned int i, count, unit;
>  
> -	might_sleep();
> -	for (i = 0; i < nr_pages; i++) {
> +	unit = preempt_model_preemptible() ? npages : PAGE_CONTIG_NR;

Almost nothing uses preempt_model_preemptible() and I'm not usefully
familiar with it.  Will this check avoid all softlockup/rcu/etc
detections in all situations (ie, configs)?

> +	for (i = 0; i < npages; ) {
> +		count = min(unit, npages - i);
> +		clear_user_highpages(nth_page(page, i),
> +				     addr + i * PAGE_SIZE, count);
> +		i += count;
>  		cond_resched();
> -		clear_user_highpage(folio_page(folio, i), addr + i * PAGE_SIZE);
>  	}
>  }

Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Ankur Arora]

Arnaldo Carvalho de Melo <acme@kernel.org> writes:

> On Wed, Sep 17, 2025 at 08:24:02AM -0700, Ankur Arora wrote:
>> This series adds clearing of contiguous page ranges for hugepages,
>> improving on the current page-at-a-time approach in two ways:
>>
>>  - amortizes the per-page setup cost over a larger extent
>>
>>  - when using string instructions, exposes the real region size
>>    to the processor.
>>
>> A processor could use a knowledge of the extent to optimize the
>> clearing. AMD Zen uarchs, as an example, elide allocation of
>> cachelines for regions larger than L3-size.
>>
>> Demand faulting a 64GB region shows performance improvements:
>>
>>  $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5
>>
>>                  mm/folio_zero_user    x86/folio_zero_user       change
>>                   (GB/s  +- %stdev)     (GB/s  +- %stdev)
>>
>>    pg-sz=2MB       11.82  +- 0.67%        16.48  +-  0.30%       + 39.4%	preempt=*
>>
>>    pg-sz=1GB       17.14  +- 1.39%        17.42  +-  0.98% [#]   +  1.6%	preempt=none|voluntary
>>    pg-sz=1GB       17.51  +- 1.19%        43.23  +-  5.22%       +146.8%	preempt=full|lazy
>>
>> [#] Milan uses a threshold of LLC-size (~32MB) for eliding cacheline
>> allocation, which is higher than the maximum extent used on x86
>> (ARCH_CONTIG_PAGE_NR=8MB), so preempt=none|voluntary sees no improvement
>> with pg-sz=1GB.
>
> I'm picking up the tools/perf part for perf-tools-next (v6.18), already
> almost 100% reviewed by Namhyung.

Thanks!

--
ankur

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[Ankur Arora]

[ Added Paul McKenney. ]

Andrew Morton <akpm@linux-foundation.org> writes:

> On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora <ankur.a.arora@oracle.com> wrote:
>
>> Change folio_zero_user() to clear contiguous page ranges instead of
>> clearing using the current page-at-a-time approach. Exposing the largest
>> feasible length can be useful in enabling processors to optimize based
>> on extent.
>
> This patch is something which MM developers might care to take a closer
> look at.
>
>> However, clearing in large chunks can have two problems:
>>
>>  - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>>    (larger folios don't have any expectation of cache locality).
>>
>>  - preemption latency when clearing large folios.
>>
>> Handle the first by splitting the clearing in three parts: the
>> faulting page and its immediate locality, its left and right
>> regions; with the local neighbourhood cleared last.
>
> Has this optimization been shown to be beneficial?

So, this was mostly meant to be defensive. The current code does a
rather extensive left-right dance around the faulting page via
c6ddfb6c58 ("mm, clear_huge_page: move order algorithm into a separate
function") and I wanted to keep the cache hot property for the region
closest to the address touched by the user.

But, no I haven't run any tests showing that it helps.

> If so, are you able to share some measurements?

From some quick kernel builds (with THP) I do see a consistent
difference of a few seconds (1% worse) if I remove this optimization.
(I'm not sure right now why it is worse -- my expectation was that we
would have higher cache misses, but I see pretty similar cache numbers.)

But let me do a more careful test and report back.

> If not, maybe it should be removed?
>
>> ...
>>
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -7021,40 +7021,80 @@ static inline int process_huge_page(
>>  	return 0;
>>  }
>>
>> -static void clear_gigantic_page(struct folio *folio, unsigned long addr_hint,
>> -				unsigned int nr_pages)
>> +/*
>> + * Clear contiguous pages chunking them up when running under
>> + * non-preemptible models.
>> + */
>> +static void clear_contig_highpages(struct page *page, unsigned long addr,
>> +				   unsigned int npages)
>
> Called "_highpages" because it wraps clear_user_highpages().  It really
> should be called clear_contig_user_highpages() ;)  (Not serious)

Or maybe clear_user_contig_highpages(), so when we get rid of HUGEMEM,
the _highpages could just be chopped off :D.

>>  {
>> -	unsigned long addr = ALIGN_DOWN(addr_hint, folio_size(folio));
>> -	int i;
>> +	unsigned int i, count, unit;
>>
>> -	might_sleep();
>> -	for (i = 0; i < nr_pages; i++) {
>> +	unit = preempt_model_preemptible() ? npages : PAGE_CONTIG_NR;
>
> Almost nothing uses preempt_model_preemptible() and I'm not usefully
> familiar with it.  Will this check avoid all softlockup/rcu/etc
> detections in all situations (ie, configs)?

IMO, yes. The code invoked under preempt_model_preemptible() will boil
down to a single interruptible REP STOSB which might execute over
an extent of 1GB (with the last patch). From prior experiments, I know
that irqs are able to interrupt this. And, I /think/ that is a sufficient
condition for avoiding RCU stalls/softlockups etc.

Also, when we were discussing lazy preemption (which Thomas had
suggested as a way to handle scenarios like this or long running Xen
hypercalls etc) this seemed like a scenario that didn't need any extra
handling for CONFIG_PREEMPT.
We did need 83b28cfe79 ("rcu: handle quiescent states for PREEMPT_RCU=n,
PREEMPT_COUNT=y") for CONFIG_PREEMPT_LAZY but AFAICS this should be safe.

Anyway let me think about your all configs point (though only ones which
can have some flavour for hugetlb.)

Also, I would like x86 folks opinion on this. And, maybe Paul McKenney
just to make sure I'm not missing something on RCU side.


Thanks for the comments.

--
ankur

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[kernel test robot]

Hi Ankur,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Ankur-Arora/perf-bench-mem-Remove-repetition-around-time-measurement/20250917-233045
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250917152418.4077386-14-ankur.a.arora%40oracle.com
patch subject: [PATCH v7 13/16] mm: memory: support clearing page ranges
config: arm-randconfig-001-20250919 (https://download.01.org/0day-ci/archive/20250919/202509191916.a0oRRfua-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 12.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250919/202509191916.a0oRRfua-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509191916.a0oRRfua-lkp@intel.com/

All error/warnings (new ones prefixed by >>):

   In file included from arch/arm/include/asm/thread_info.h:14,
                    from include/linux/thread_info.h:60,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/arm/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:79,
                    from include/linux/smp.h:116,
                    from include/linux/kernel_stat.h:5,
                    from mm/memory.c:42:
   mm/memory.c: In function 'clear_contig_highpages':
   mm/memory.c:7199:38: error: implicit declaration of function 'nth_page'; did you mean 'pte_page'? [-Werror=implicit-function-declaration]
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                                      ^~~~~~~~
   arch/arm/include/asm/page.h:152:36: note: in definition of macro 'clear_user_highpage'
     152 |          __cpu_clear_user_highpage(page, vaddr)
         |                                    ^~~~
   mm/memory.c:7199:17: note: in expansion of macro 'clear_user_highpages'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                 ^~~~~~~~~~~~~~~~~~~~
>> mm/memory.c:7199:38: warning: passing argument 1 of 'cpu_user.cpu_clear_user_highpage' makes pointer from integer without a cast [-Wint-conversion]
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                                      ^~~~~~~~~~~~~~~~~
         |                                      |
         |                                      int
   arch/arm/include/asm/page.h:152:36: note: in definition of macro 'clear_user_highpage'
     152 |          __cpu_clear_user_highpage(page, vaddr)
         |                                    ^~~~
   mm/memory.c:7199:17: note: in expansion of macro 'clear_user_highpages'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                 ^~~~~~~~~~~~~~~~~~~~
   mm/memory.c:7199:38: note: expected 'struct page *' but argument is of type 'int'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                                      ^~~~~~~~~~~~~~~~~
   arch/arm/include/asm/page.h:152:36: note: in definition of macro 'clear_user_highpage'
     152 |          __cpu_clear_user_highpage(page, vaddr)
         |                                    ^~~~
   mm/memory.c:7199:17: note: in expansion of macro 'clear_user_highpages'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                 ^~~~~~~~~~~~~~~~~~~~
>> arch/arm/include/asm/page.h:157:15: error: lvalue required as left operand of assignment
     157 |         vaddr += PAGE_SIZE;                             \
         |               ^~
   mm/memory.c:7199:17: note: in expansion of macro 'clear_user_highpages'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                 ^~~~~~~~~~~~~~~~~~~~
>> arch/arm/include/asm/page.h:158:13: error: lvalue required as increment operand
     158 |         page++;                                         \
         |             ^~
   mm/memory.c:7199:17: note: in expansion of macro 'clear_user_highpages'
    7199 |                 clear_user_highpages(nth_page(page, i),
         |                 ^~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +7199 mm/memory.c

  7185	
  7186	/*
  7187	 * Clear contiguous pages chunking them up when running under
  7188	 * non-preemptible models.
  7189	 */
  7190	static void clear_contig_highpages(struct page *page, unsigned long addr,
  7191					   unsigned int npages)
  7192	{
  7193		unsigned int i, count, unit;
  7194	
  7195		unit = preempt_model_preemptible() ? npages : PAGE_CONTIG_NR;
  7196	
  7197		for (i = 0; i < npages; ) {
  7198			count = min(unit, npages - i);
> 7199			clear_user_highpages(nth_page(page, i),
  7200					     addr + i * PAGE_SIZE, count);
  7201			i += count;
  7202			cond_resched();
  7203		}
  7204	}
  7205	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Raghavendra K T]

On 9/17/2025 8:54 PM, Ankur Arora wrote:
> This series adds clearing of contiguous page ranges for hugepages,
> improving on the current page-at-a-time approach in two ways:
> 
>   - amortizes the per-page setup cost over a larger extent
> 
>   - when using string instructions, exposes the real region size
>     to the processor.
> 
> A processor could use a knowledge of the extent to optimize the
> clearing. AMD Zen uarchs, as an example, elide allocation of
> cachelines for regions larger than L3-size.
[...]

Hello,

Feel free to add

Tested-by: Raghavendra K T <raghavendra.kt@amd.com>
 
for whole series.

[ I do understand that there may be minor tweeks to clear page patches
to convert nth_page once David's changes are in]

SUT: AMD Zen5

I also did a quick hack to unconditionally use CLZERO/MOVNT on top of
Ankur's series to test how much additional benefits can architectural
enhancements bring in. [ Inline with second part of Ankur's old series before
preempt lazy changes ]. Please note that it is only for testing ideally
for lower sizes we would want rep stosb only. and threshold at which
we need to do non-temporal copy should be a function of L3 and / OR L2 size
perhaps.

Results:
base      : 6.17-rc6 + perf bench patches
clearpage : 6.17-rc6 + whole series from Ankur 
clzero    : 6.17-rc6 + Ankur's series +  clzero (below patch)
movnt     : 6.17-rc6 + Ankur's series +  movnt (below patch)

Command run: ./perf bench mem mmap -p 2MB -f demand -s 64GB -l 10

Higher = better

                   preempt = lazy (GB/sec)  preempt = voluntary (GB/sec)

base               20.655559                19.712500

clearpage          35.060572                34.533414      

clzero             66.948422                66.067265

movnt              51.593506                51.403765


CLZERO/MOVNT experimental patch. Hope I have not missed anything here :)

-- >8 --
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 52c8910ba2ef..26cef2b187b9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -3170,6 +3170,8 @@ config HAVE_ATOMIC_IOMAP
 	def_bool y
 	depends on X86_32
 
+source "arch/x86/Kconfig.cpy"
+
 source "arch/x86/kvm/Kconfig"
 
 source "arch/x86/Kconfig.cpufeatures"
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 2361066d175e..aa2e62bbfa62 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -84,11 +84,23 @@ static inline void clear_pages(void *addr, unsigned int npages)
 	 */
 	kmsan_unpoison_memory(addr, len);
 	asm volatile(ALTERNATIVE_2("call memzero_page_aligned_unrolled",
-				   "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
-				   "rep stosb", X86_FEATURE_ERMS)
-			: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
-			: "a" (0)
-			: "cc", "memory");
+				"shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
+#if defined(CONFIG_CLEARPAGE_CLZERO)
+		"call clear_pages_clzero", X86_FEATURE_CLZERO)
+		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
+		: "a" (0)
+		: "cc", "memory");
+#elif defined(CONFIG_CLEARPAGE_MOVNT)
+		"call clear_pages_movnt", X86_FEATURE_XMM2)
+		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
+		: "a" (0)
+		: "cc", "memory");
+#else
+		"rep stosb", X86_FEATURE_ERMS)
+		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
+		: "a" (0)
+		: "cc", "memory");
+#endif
 }
 #define clear_pages clear_pages
 
diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index 27debe0c018c..0848287446dd 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -4,6 +4,7 @@
 #include <linux/cfi_types.h>
 #include <linux/objtool.h>
 #include <asm/asm.h>
+#include <asm/page_types.h>
 
 /*
  * Zero page aligned region.
@@ -119,3 +120,40 @@ SYM_FUNC_START(rep_stos_alternative)
 	_ASM_EXTABLE_UA(17b, .Lclear_user_tail)
 SYM_FUNC_END(rep_stos_alternative)
 EXPORT_SYMBOL(rep_stos_alternative)
+
+SYM_FUNC_START(clear_pages_movnt)
+	.p2align 4
+.Lstart:
+	movnti  %rax, 0x00(%rdi)
+	movnti  %rax, 0x08(%rdi)
+	movnti  %rax, 0x10(%rdi)
+	movnti  %rax, 0x18(%rdi)
+	movnti  %rax, 0x20(%rdi)
+	movnti  %rax, 0x28(%rdi)
+	movnti  %rax, 0x30(%rdi)
+	movnti  %rax, 0x38(%rdi)
+	addq    $0x40, %rdi
+	subl    $0x40, %ecx
+	ja      .Lstart
+	RET
+SYM_FUNC_END(clear_pages_movnt)
+EXPORT_SYMBOL_GPL(clear_pages_movnt)
+
+/*
+ * Zero a page using clzero (On AMD, with CPU_FEATURE_CLZERO.)
+ *
+ * Caller needs to issue a sfence at the end.
+ */
+
+SYM_FUNC_START(clear_pages_clzero)
+	movq	%rdi,%rax
+	.p2align 4
+.Liter:
+	clzero
+	addq    $0x40, %rax
+	subl    $0x40, %ecx
+	ja      .Liter
+	sfence
+	RET
+SYM_FUNC_END(clear_pages_clzero)
+EXPORT_SYMBOL_GPL(clear_pages_clzero)
-- 
2.43.0

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[David Hildenbrand]

On 17.09.25 17:24, Ankur Arora wrote:
> Define fallback versions of clear_pages(), clear_user_pages().
> 
> In absence of architectural primitives, we just clear pages
> sequentially.
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
>   include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>   1 file changed, 38 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1ae97a0b8ec7..0cde9b01da5e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>   				unsigned int order) {}
>   #endif	/* CONFIG_DEBUG_PAGEALLOC */
>   
> +#ifndef clear_pages
> +/**
> + * clear_pages() - clear a page range using a kernel virtual address.

I'd just call this "clear a page range for kernel-internal use"

> + * @addr: start address
> + * @npages: number of pages
> + *
> + * Assumes that (@addr, +@npages) references a kernel region.

And say here simply that "Use clear_user_pages() instead for clearing a 
page range to be mapped to user space".

> + * Does absolutely no exception handling.
> + */
> +static inline void clear_pages(void *addr, unsigned int npages)
> +{
> +	do {
> +		clear_page(addr);
> +		addr += PAGE_SIZE;
> +	} while (--npages);
> +}
> +#endif
> +
> +#ifndef clear_user_pages
> +/**
> + * clear_user_pages() - clear a page range mapped by the user.

I'd call this then "clear a page range to be mapped to user space"

Because it's usually called before we actually map it and it will 
properly flush the dcache if required.

> + * @addr: kernel mapped address

"start address"

> + * @vaddr: user mapped address

"start address of the user mapping" ?

> + * @pg: start page

Please just call it "page". I know, clear_user_page() has this weird 
page vs. pg thingy, but let's do it better here.

> + * @npages: number of pages
> + *
> + * Assumes that the region (@addr, +@npages) has been validated
> + * already so this does no exception handling.
> + */
> +#define clear_user_pages(addr, vaddr, pg, npages)	\
> +do {							\
> +	clear_user_page(addr, vaddr, pg);		\
> +	addr += PAGE_SIZE;				\
> +	vaddr += PAGE_SIZE;				\
> +	pg++;						\
> +} while (--npages)
> +#endif

Should indent with one tab. Any reason this is not a static inline 
function?

-- 
Cheers

David / dhildenb

Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[David Hildenbrand]

On 17.09.25 17:24, Ankur Arora wrote:
> Define clear_user_highpages() which clears pages sequentially using
> the single page variant.
> 
> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
> primitive clear_user_pages().
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
>   include/linux/highmem.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 6234f316468c..ed609987e24d 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>   }
>   #endif
>   
> +#ifndef clear_user_highpages

Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
but makes it clear that this for pages that might reside in highmem.

> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
> +					unsigned int npages)
> +{
> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
> +		clear_user_pages(base, vaddr, page, npages);

Single line should work

		clear_user_pages(page_address(page), vaddr, page, npages);

> +		return;
> +	}
> +
> +	do {
> +		clear_user_highpage(page, vaddr);
> +		vaddr += PAGE_SIZE;
> +		page++;
> +	} while (--npages);
> +}
> +#endif
> +
>   #ifndef vma_alloc_zeroed_movable_folio
>   /**
>    * vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.


-- 
Cheers

David / dhildenb

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[David Hildenbrand]

On 17.09.25 17:24, Ankur Arora wrote:
> For configurations with CONFIG_MMU we do not define clear_user_page().
> This runs into issues for configurations with !CONFIG_HIGHMEM, because
> clear_user_highpages() expects to clear_user_page() (via a default
> version of clear_user_pages()).

I'm confused. Can you elaborate once more why we cannot take care of 
that in common code?

If it's about clear_user_pages(), then you can just switch from 
!IS_ENABLED(CONFIG_HIGHMEM) to ifdef in patch #11.

-- 
Cheers

David / dhildenb

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[David Hildenbrand]

On 17.09.25 23:44, Andrew Morton wrote:
> On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora <ankur.a.arora@oracle.com> wrote:
> 
>> Change folio_zero_user() to clear contiguous page ranges instead of
>> clearing using the current page-at-a-time approach. Exposing the largest
>> feasible length can be useful in enabling processors to optimize based
>> on extent.
> 
> This patch is something which MM developers might care to take a closer
> look at.

I took a look at various revisions of this series, I'm only lagging 
behind on reviewing the latest series :)

> 
>> However, clearing in large chunks can have two problems:
>>
>>   - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>>     (larger folios don't have any expectation of cache locality).
>>
>>   - preemption latency when clearing large folios.
>>
>> Handle the first by splitting the clearing in three parts: the
>> faulting page and its immediate locality, its left and right
>> regions; with the local neighbourhood cleared last.
> 
> Has this optimization been shown to be beneficial?
> 
> If so, are you able to share some measurements?
> 
> If not, maybe it should be removed?
> 
>> ...
>>
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -7021,40 +7021,80 @@ static inline int process_huge_page(
>>   	return 0;
>>   }
>>   
>> -static void clear_gigantic_page(struct folio *folio, unsigned long addr_hint,
>> -				unsigned int nr_pages)
>> +/*
>> + * Clear contiguous pages chunking them up when running under
>> + * non-preemptible models.
>> + */
>> +static void clear_contig_highpages(struct page *page, unsigned long addr,
>> +				   unsigned int npages)
> 
> Called "_highpages" because it wraps clear_user_highpages().  It really
> should be called clear_contig_user_highpages() ;)  (Not serious)

You have a point there, though :)

Fortunately this is only an internal helper.

-- 
Cheers

David / dhildenb

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[Raghavendra K T]

On 9/18/2025 3:14 AM, Andrew Morton wrote:
> On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora <ankur.a.arora@oracle.com> wrote:
> 
>> Change folio_zero_user() to clear contiguous page ranges instead of
>> clearing using the current page-at-a-time approach. Exposing the largest
>> feasible length can be useful in enabling processors to optimize based
>> on extent.
> 
> This patch is something which MM developers might care to take a closer
> look at.
> 
>> However, clearing in large chunks can have two problems:
>>
>>   - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>>     (larger folios don't have any expectation of cache locality).
>>
>>   - preemption latency when clearing large folios.
>>
>> Handle the first by splitting the clearing in three parts: the
>> faulting page and its immediate locality, its left and right
>> regions; with the local neighbourhood cleared last.
> 
> Has this optimization been shown to be beneficial?
> 
> If so, are you able to share some measurements?
> 
> If not, maybe it should be removed?
> 

I reverted the effect of this patch by hard coding

#define PAGE_CONTIG_NR 1

I see that benefit for voluntary kernel is lost without this change

(for rep stosb)

with PAGE_CONTIG_NR equivalent to 8MB

Preempt mode: voluntary

# Running 'mem/mmap' benchmark:
# function 'demand' (Demand loaded mmap())
# Copying 64GB bytes ...

       34.533414 GB/sec


with PAGE_CONTIG_NR equivalent to 4KB

# Running 'mem/mmap' benchmark:
# function 'demand' (Demand loaded mmap())
# Copying 64GB bytes ...

       20.766059 GB/sec

For now (barring David's recommendations),
feel free to add

Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[Raghavendra K T]

On 9/23/2025 2:06 PM, Raghavendra K T wrote:
> 
> 
> On 9/18/2025 3:14 AM, Andrew Morton wrote:
>> On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora 
>> <ankur.a.arora@oracle.com> wrote:
>>
>>> Change folio_zero_user() to clear contiguous page ranges instead of
>>> clearing using the current page-at-a-time approach. Exposing the largest
>>> feasible length can be useful in enabling processors to optimize based
>>> on extent.
>>
>> This patch is something which MM developers might care to take a closer
>> look at.
>>
>>> However, clearing in large chunks can have two problems:
>>>
>>>   - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>>>     (larger folios don't have any expectation of cache locality).
>>>
>>>   - preemption latency when clearing large folios.
>>>
>>> Handle the first by splitting the clearing in three parts: the
>>> faulting page and its immediate locality, its left and right
>>> regions; with the local neighbourhood cleared last.
>>
>> Has this optimization been shown to be beneficial?
>>
>> If so, are you able to share some measurements?
>>
>> If not, maybe it should be removed?
>>
> 
> I reverted the effect of this patch by hard coding
> 
> #define PAGE_CONTIG_NR 1
> 
> I see that benefit for voluntary kernel is lost without this change
> 
> (for rep stosb)
> 
> with PAGE_CONTIG_NR equivalent to 8MB
> 
> Preempt mode: voluntary
> 
> # Running 'mem/mmap' benchmark:
> # function 'demand' (Demand loaded mmap())
> # Copying 64GB bytes ...
> 
>        34.533414 GB/sec
> 
> 
> with PAGE_CONTIG_NR equivalent to 4KB
> 
> # Running 'mem/mmap' benchmark:
> # function 'demand' (Demand loaded mmap())
> # Copying 64GB bytes ...
> 
>        20.766059 GB/sec
> 
> For now (barring David's recommendations),
> feel free to add
> 
> Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>
> 
> 

My reply was more towards the benefits of clearing multiple pages
for non-preempt and voluntary kernel, than the effect of clearing
neighborhood range at the end.

Sorry if that was confusing :)

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 17.09.25 17:24, Ankur Arora wrote:
>> Define fallback versions of clear_pages(), clear_user_pages().
>> In absence of architectural primitives, we just clear pages
>> sequentially.
>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>> ---
>>   include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 38 insertions(+)
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>   				unsigned int order) {}
>>   #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>   +#ifndef clear_pages
>> +/**
>> + * clear_pages() - clear a page range using a kernel virtual address.
>
> I'd just call this "clear a page range for kernel-internal use"
>
>> + * @addr: start address
>> + * @npages: number of pages
>> + *
>> + * Assumes that (@addr, +@npages) references a kernel region.
>
> And say here simply that "Use clear_user_pages() instead for clearing a page
> range to be mapped to user space".

So, comments that actually speak to the use instead of technically
correct but unhelpful generalities :). Thanks, good lesson.

>> + * Does absolutely no exception handling.
>> + */
>> +static inline void clear_pages(void *addr, unsigned int npages)
>> +{
>> +	do {
>> +		clear_page(addr);
>> +		addr += PAGE_SIZE;
>> +	} while (--npages);
>> +}
>> +#endif
>> +
>> +#ifndef clear_user_pages
>> +/**
>> + * clear_user_pages() - clear a page range mapped by the user.
>
> I'd call this then "clear a page range to be mapped to user space"
>
> Because it's usually called before we actually map it and it will properly flush
> the dcache if required.

Makes sense.

>> + * @addr: kernel mapped address
>
> "start address"
>
>> + * @vaddr: user mapped address
>
> "start address of the user mapping" ?
>
>> + * @pg: start page
>
> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
> thingy, but let's do it better here.
>
>> + * @npages: number of pages
>> + *
>> + * Assumes that the region (@addr, +@npages) has been validated
>> + * already so this does no exception handling.
>> + */
>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>> +do {							\
>> +	clear_user_page(addr, vaddr, pg);		\
>> +	addr += PAGE_SIZE;				\
>> +	vaddr += PAGE_SIZE;				\
>> +	pg++;						\
>> +} while (--npages)
>> +#endif
>
> Should indent with one tab.

Will do. Also acking to the ones above.

> Any reason this is not a static inline function?

Alas yes. Most architecture code defines clear_user_page() as a macro
where, if they need a to flush the dcache or otherwise do something
special, they need access to some external primitive. And this primitive
which might not be visible in contexts that we include this header.

For instance this one on sparc:
  https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/

Defining as a macro to get around that. But maybe there's a better
way?

--
ankur

Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 17.09.25 17:24, Ankur Arora wrote:
>> Define clear_user_highpages() which clears pages sequentially using
>> the single page variant.
>> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
>> primitive clear_user_pages().
>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>> ---
>>   include/linux/highmem.h | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
>> index 6234f316468c..ed609987e24d 100644
>> --- a/include/linux/highmem.h
>> +++ b/include/linux/highmem.h
>> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>>   }
>>   #endif
>>   +#ifndef clear_user_highpages
>
> Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
> but makes it clear that this for pages that might reside in highmem.

Didn't add one because clear_user_highpage() didn't have one. Will add
for both.

>> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>> +					unsigned int npages)
>> +{
>> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>> +		clear_user_pages(base, vaddr, page, npages);
>
> Single line should work
>
> 		clear_user_pages(page_address(page), vaddr, page, npages);

Unfortunately not. The problem is that I'm defining the fallback version
of clear_user_pages() as a macro in the previous patch.

        +#define clear_user_pages(addr, vaddr, pg, npages)	\
        +do {							\
        +	clear_user_page(addr, vaddr, pg);		\
        +	addr += PAGE_SIZE;				\
        +	vaddr += PAGE_SIZE;				\
        +	pg++;						\
        +} while (--npages)


And so using page_address() directly doesn't work because addr needs
to be an lvalue for the addition which page_address(page) isn't.


Thanks

--
ankur

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 17.09.25 17:24, Ankur Arora wrote:
>> For configurations with CONFIG_MMU we do not define clear_user_page().
>> This runs into issues for configurations with !CONFIG_HIGHMEM, because
>> clear_user_highpages() expects to clear_user_page() (via a default
>> version of clear_user_pages()).
>
> I'm confused. Can you elaborate once more why we cannot take care of that in
> common code?

So my definition of clear_user_highpages,

    +#ifndef clear_user_highpages
    +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
    +					unsigned int npages)
    +{
    +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
    +		void *base = page_address(page);
    +		clear_user_pages(base, vaddr, page, npages);
    +		return;
    +	}
    +
    +	do {
    +		clear_user_highpage(page, vaddr);
    +		vaddr += PAGE_SIZE;
    +		page++;
    +	} while (--npages);
    +}
    +#endif

assumes one of the following:

  1. clear_user_highpages is defined by the architecture or,
  2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
  3. !HIGHMEM => arch defines clear_user_pages or clear_user_page

Case 2 is fine, since ARM has clear_user_highpage().

Case 3 runs into a problem since ARM doesn't have clear_user_pages()
or clear_user_page() (it does have the second, but only with !CONFIG_MMU).

> If it's about clear_user_pages(), then you can just switch from
> !IS_ENABLED(CONFIG_HIGHMEM) to ifdef in patch #11.

It's worse than just clear_user_pages(), since we will have
clear_user_pages() (due to the defintion in patch-10) but that
is broken since the arch doesn't define clear_user_page().

I think the fallback defintions of clear_user_highpages() and
clear_user_pages() are reasonably sane so this needs to be addressed
in the arch code.

I defined clear_user_highpages() since it already has clear_user_highpage().

Another solution might be to define clear_user_page() for ARM which
would also address the broken-ness of clear_user_pages() but that
is more intrusive since that needs actual knowledge of the ARM mapping
model(s).

--
ankur

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[David Hildenbrand]

On 23.09.25 22:26, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 17.09.25 17:24, Ankur Arora wrote:
>>> Define fallback versions of clear_pages(), clear_user_pages().
>>> In absence of architectural primitives, we just clear pages
>>> sequentially.
>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>> ---
>>>    include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>    1 file changed, 38 insertions(+)
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>>    				unsigned int order) {}
>>>    #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>>    +#ifndef clear_pages
>>> +/**
>>> + * clear_pages() - clear a page range using a kernel virtual address.
>>
>> I'd just call this "clear a page range for kernel-internal use"
>>
>>> + * @addr: start address
>>> + * @npages: number of pages
>>> + *
>>> + * Assumes that (@addr, +@npages) references a kernel region.
>>
>> And say here simply that "Use clear_user_pages() instead for clearing a page
>> range to be mapped to user space".
> 
> So, comments that actually speak to the use instead of technically
> correct but unhelpful generalities :). Thanks, good lesson.
> 
>>> + * Does absolutely no exception handling.
>>> + */
>>> +static inline void clear_pages(void *addr, unsigned int npages)
>>> +{
>>> +	do {
>>> +		clear_page(addr);
>>> +		addr += PAGE_SIZE;
>>> +	} while (--npages);
>>> +}
>>> +#endif
>>> +
>>> +#ifndef clear_user_pages
>>> +/**
>>> + * clear_user_pages() - clear a page range mapped by the user.
>>
>> I'd call this then "clear a page range to be mapped to user space"
>>
>> Because it's usually called before we actually map it and it will properly flush
>> the dcache if required.
> 
> Makes sense.
> 
>>> + * @addr: kernel mapped address
>>
>> "start address"
>>
>>> + * @vaddr: user mapped address
>>
>> "start address of the user mapping" ?
>>
>>> + * @pg: start page
>>
>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
>> thingy, but let's do it better here.
>>
>>> + * @npages: number of pages
>>> + *
>>> + * Assumes that the region (@addr, +@npages) has been validated
>>> + * already so this does no exception handling.
>>> + */
>>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>>> +do {							\
>>> +	clear_user_page(addr, vaddr, pg);		\
>>> +	addr += PAGE_SIZE;				\
>>> +	vaddr += PAGE_SIZE;				\
>>> +	pg++;						\
>>> +} while (--npages)
>>> +#endif
>>
>> Should indent with one tab.
> 
> Will do. Also acking to the ones above.
> 
>> Any reason this is not a static inline function?
> 
> Alas yes. Most architecture code defines clear_user_page() as a macro
> where, if they need a to flush the dcache or otherwise do something
> special, they need access to some external primitive. And this primitive
> which might not be visible in contexts that we include this header.
> 
> For instance this one on sparc:
>    https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/
> 
> Defining as a macro to get around that. But maybe there's a better
> way?

Can we just move it to mm/utils.c and not have it be an inline function?


-- 
Cheers

David / dhildenb

Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[David Hildenbrand]

On 23.09.25 22:34, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 17.09.25 17:24, Ankur Arora wrote:
>>> Define clear_user_highpages() which clears pages sequentially using
>>> the single page variant.
>>> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
>>> primitive clear_user_pages().
>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>> ---
>>>    include/linux/highmem.h | 18 ++++++++++++++++++
>>>    1 file changed, 18 insertions(+)
>>> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
>>> index 6234f316468c..ed609987e24d 100644
>>> --- a/include/linux/highmem.h
>>> +++ b/include/linux/highmem.h
>>> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>>>    }
>>>    #endif
>>>    +#ifndef clear_user_highpages
>>
>> Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
>> but makes it clear that this for pages that might reside in highmem.
> 
> Didn't add one because clear_user_highpage() didn't have one. Will add
> for both.
> 

Doesn't have to be excessive. But even I have to keep reminding myself 
when to use clear_page(), clear_user_page(), clear_user_highpage() ...

>>> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>>> +					unsigned int npages)
>>> +{
>>> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>>> +		clear_user_pages(base, vaddr, page, npages);
>>
>> Single line should work
>>
>> 		clear_user_pages(page_address(page), vaddr, page, npages);
> 
> Unfortunately not. The problem is that I'm defining the fallback version
> of clear_user_pages() as a macro in the previous patch.

Yet another sign that we have to fix that instead. :)

-- 
Cheers

David / dhildenb

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[David Hildenbrand]

On 24.09.25 00:25, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 17.09.25 17:24, Ankur Arora wrote:
>>> For configurations with CONFIG_MMU we do not define clear_user_page().
>>> This runs into issues for configurations with !CONFIG_HIGHMEM, because
>>> clear_user_highpages() expects to clear_user_page() (via a default
>>> version of clear_user_pages()).
>>
>> I'm confused. Can you elaborate once more why we cannot take care of that in
>> common code?
> 
> So my definition of clear_user_highpages,
> 
>      +#ifndef clear_user_highpages
>      +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>      +					unsigned int npages)
>      +{
>      +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>      +		void *base = page_address(page);
>      +		clear_user_pages(base, vaddr, page, npages);
>      +		return;
>      +	}
>      +
>      +	do {
>      +		clear_user_highpage(page, vaddr);
>      +		vaddr += PAGE_SIZE;
>      +		page++;
>      +	} while (--npages);
>      +}
>      +#endif
> 
> assumes one of the following:
> 
>    1. clear_user_highpages is defined by the architecture or,
>    2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
>    3. !HIGHMEM => arch defines clear_user_pages or clear_user_page
> 
> Case 2 is fine, since ARM has clear_user_highpage().
> 
> Case 3 runs into a problem since ARM doesn't have clear_user_pages()
> or clear_user_page() (it does have the second, but only with !CONFIG_MMU).

I think we should look into having a generic fallback version in common 
code instead for that case, and not require the arch to implement such a 
loop around clear_user_highpage().

-- 
Cheers

David / dhildenb

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 23.09.25 22:26, Ankur Arora wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>> Define fallback versions of clear_pages(), clear_user_pages().
>>>> In absence of architectural primitives, we just clear pages
>>>> sequentially.
>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>> ---
>>>>    include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 38 insertions(+)
>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>>>> --- a/include/linux/mm.h
>>>> +++ b/include/linux/mm.h
>>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>>>    				unsigned int order) {}
>>>>    #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>>>    +#ifndef clear_pages
>>>> +/**
>>>> + * clear_pages() - clear a page range using a kernel virtual address.
>>>
>>> I'd just call this "clear a page range for kernel-internal use"
>>>
>>>> + * @addr: start address
>>>> + * @npages: number of pages
>>>> + *
>>>> + * Assumes that (@addr, +@npages) references a kernel region.
>>>
>>> And say here simply that "Use clear_user_pages() instead for clearing a page
>>> range to be mapped to user space".
>> So, comments that actually speak to the use instead of technically
>> correct but unhelpful generalities :). Thanks, good lesson.
>>
>>>> + * Does absolutely no exception handling.
>>>> + */
>>>> +static inline void clear_pages(void *addr, unsigned int npages)
>>>> +{
>>>> +	do {
>>>> +		clear_page(addr);
>>>> +		addr += PAGE_SIZE;
>>>> +	} while (--npages);
>>>> +}
>>>> +#endif
>>>> +
>>>> +#ifndef clear_user_pages
>>>> +/**
>>>> + * clear_user_pages() - clear a page range mapped by the user.
>>>
>>> I'd call this then "clear a page range to be mapped to user space"
>>>
>>> Because it's usually called before we actually map it and it will properly flush
>>> the dcache if required.
>> Makes sense.
>>
>>>> + * @addr: kernel mapped address
>>>
>>> "start address"
>>>
>>>> + * @vaddr: user mapped address
>>>
>>> "start address of the user mapping" ?
>>>
>>>> + * @pg: start page
>>>
>>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
>>> thingy, but let's do it better here.
>>>
>>>> + * @npages: number of pages
>>>> + *
>>>> + * Assumes that the region (@addr, +@npages) has been validated
>>>> + * already so this does no exception handling.
>>>> + */
>>>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>>>> +do {							\
>>>> +	clear_user_page(addr, vaddr, pg);		\
>>>> +	addr += PAGE_SIZE;				\
>>>> +	vaddr += PAGE_SIZE;				\
>>>> +	pg++;						\
>>>> +} while (--npages)
>>>> +#endif
>>>
>>> Should indent with one tab.
>> Will do. Also acking to the ones above.
>>
>>> Any reason this is not a static inline function?
>> Alas yes. Most architecture code defines clear_user_page() as a macro
>> where, if they need a to flush the dcache or otherwise do something
>> special, they need access to some external primitive. And this primitive
>> which might not be visible in contexts that we include this header.
>> For instance this one on sparc:
>>    https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/
>> Defining as a macro to get around that. But maybe there's a better
>> way?
>
> Can we just move it to mm/utils.c and not have it be an inline function?

Thanks. Yeah, that's a good place for it.

--
ankur

Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 23.09.25 22:34, Ankur Arora wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>> Define clear_user_highpages() which clears pages sequentially using
>>>> the single page variant.
>>>> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
>>>> primitive clear_user_pages().
>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>> ---
>>>>    include/linux/highmem.h | 18 ++++++++++++++++++
>>>>    1 file changed, 18 insertions(+)
>>>> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
>>>> index 6234f316468c..ed609987e24d 100644
>>>> --- a/include/linux/highmem.h
>>>> +++ b/include/linux/highmem.h
>>>> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>>>>    }
>>>>    #endif
>>>>    +#ifndef clear_user_highpages
>>>
>>> Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
>>> but makes it clear that this for pages that might reside in highmem.
>> Didn't add one because clear_user_highpage() didn't have one. Will add
>> for both.
>>
>
> Doesn't have to be excessive. But even I have to keep reminding myself when to
> use clear_page(), clear_user_page(), clear_user_highpage() ...

And now all the multi-page variants. Really motivates the removal of
the HIGHMEM stuff.

>>>> +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>>>> +					unsigned int npages)
>>>> +{
>>>> +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>>>> +		clear_user_pages(base, vaddr, page, npages);
>>>
>>> Single line should work
>>>
>>> 		clear_user_pages(page_address(page), vaddr, page, npages);
>> Unfortunately not. The problem is that I'm defining the fallback version
>> of clear_user_pages() as a macro in the previous patch.
>
> Yet another sign that we have to fix that instead. :)

Yeah :).

Thanks
--
ankur

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

> On 24.09.25 00:25, Ankur Arora wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>> For configurations with CONFIG_MMU we do not define clear_user_page().
>>>> This runs into issues for configurations with !CONFIG_HIGHMEM, because
>>>> clear_user_highpages() expects to clear_user_page() (via a default
>>>> version of clear_user_pages()).
>>>
>>> I'm confused. Can you elaborate once more why we cannot take care of that in
>>> common code?
>> So my definition of clear_user_highpages,
>>      +#ifndef clear_user_highpages
>>      +static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
>>      +					unsigned int npages)
>>      +{
>>      +	if (!IS_ENABLED(CONFIG_HIGHMEM)) {
>>      +		void *base = page_address(page);
>>      +		clear_user_pages(base, vaddr, page, npages);
>>      +		return;
>>      +	}
>>      +
>>      +	do {
>>      +		clear_user_highpage(page, vaddr);
>>      +		vaddr += PAGE_SIZE;
>>      +		page++;
>>      +	} while (--npages);
>>      +}
>>      +#endif
>> assumes one of the following:
>>    1. clear_user_highpages is defined by the architecture or,
>>    2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
>>    3. !HIGHMEM => arch defines clear_user_pages or clear_user_page
>> Case 2 is fine, since ARM has clear_user_highpage().
>> Case 3 runs into a problem since ARM doesn't have clear_user_pages()
>> or clear_user_page() (it does have the second, but only with !CONFIG_MMU).
>
> I think we should look into having a generic fallback version in common code
> instead for that case, and not require the arch to implement such a loop around
> clear_user_highpage().

So, as you suggested, I moved clear_user_pages() to mm/utils.c and
conditioned it on clear_user_page() also existing.

  #if defined(clear_user_page) && !defined(clear_user_pages)
  void clear_user_pages(void *addr, unsigned long vaddr, struct page *page,
                        unsigned int npages) {
                      ...
  }
  #endif

That fixed this issue as well since there's no more bogus reference to
clear_user_page().

Are there cases in which (TRANSPARENT_HUGEPAGE || HUGETLB) might be enabled
on ARM?

--
ankur

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[David Hildenbrand]

On 25.09.25 07:25, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 23.09.25 22:26, Ankur Arora wrote:
>>> David Hildenbrand <david@redhat.com> writes:
>>>
>>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>>> Define fallback versions of clear_pages(), clear_user_pages().
>>>>> In absence of architectural primitives, we just clear pages
>>>>> sequentially.
>>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>>> ---
>>>>>     include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>>>     1 file changed, 38 insertions(+)
>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>>>>> --- a/include/linux/mm.h
>>>>> +++ b/include/linux/mm.h
>>>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>>>>     				unsigned int order) {}
>>>>>     #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>>>>     +#ifndef clear_pages
>>>>> +/**
>>>>> + * clear_pages() - clear a page range using a kernel virtual address.
>>>>
>>>> I'd just call this "clear a page range for kernel-internal use"
>>>>
>>>>> + * @addr: start address
>>>>> + * @npages: number of pages
>>>>> + *
>>>>> + * Assumes that (@addr, +@npages) references a kernel region.
>>>>
>>>> And say here simply that "Use clear_user_pages() instead for clearing a page
>>>> range to be mapped to user space".
>>> So, comments that actually speak to the use instead of technically
>>> correct but unhelpful generalities :). Thanks, good lesson.
>>>
>>>>> + * Does absolutely no exception handling.
>>>>> + */
>>>>> +static inline void clear_pages(void *addr, unsigned int npages)
>>>>> +{
>>>>> +	do {
>>>>> +		clear_page(addr);
>>>>> +		addr += PAGE_SIZE;
>>>>> +	} while (--npages);
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +#ifndef clear_user_pages
>>>>> +/**
>>>>> + * clear_user_pages() - clear a page range mapped by the user.
>>>>
>>>> I'd call this then "clear a page range to be mapped to user space"
>>>>
>>>> Because it's usually called before we actually map it and it will properly flush
>>>> the dcache if required.
>>> Makes sense.
>>>
>>>>> + * @addr: kernel mapped address
>>>>
>>>> "start address"
>>>>
>>>>> + * @vaddr: user mapped address
>>>>
>>>> "start address of the user mapping" ?
>>>>
>>>>> + * @pg: start page
>>>>
>>>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
>>>> thingy, but let's do it better here.
>>>>
>>>>> + * @npages: number of pages
>>>>> + *
>>>>> + * Assumes that the region (@addr, +@npages) has been validated
>>>>> + * already so this does no exception handling.
>>>>> + */
>>>>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>>>>> +do {							\
>>>>> +	clear_user_page(addr, vaddr, pg);		\
>>>>> +	addr += PAGE_SIZE;				\
>>>>> +	vaddr += PAGE_SIZE;				\
>>>>> +	pg++;						\
>>>>> +} while (--npages)
>>>>> +#endif
>>>>
>>>> Should indent with one tab.
>>> Will do. Also acking to the ones above.
>>>
>>>> Any reason this is not a static inline function?
>>> Alas yes. Most architecture code defines clear_user_page() as a macro
>>> where, if they need a to flush the dcache or otherwise do something
>>> special, they need access to some external primitive. And this primitive
>>> which might not be visible in contexts that we include this header.
>>> For instance this one on sparc:
>>>     https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/
>>> Defining as a macro to get around that. But maybe there's a better
>>> way?
>>
>> Can we just move it to mm/utils.c and not have it be an inline function?
> 
> Thanks. Yeah, that's a good place for it.

If the function call overhead is ever a problem, we can look into 
reworking that.

-- 
Cheers

David / dhildenb

Re: [PATCH v7 11/16] mm/highmem: introduce clear_user_highpages()

[David Hildenbrand]

On 25.09.25 07:26, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 23.09.25 22:34, Ankur Arora wrote:
>>> David Hildenbrand <david@redhat.com> writes:
>>>
>>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>>> Define clear_user_highpages() which clears pages sequentially using
>>>>> the single page variant.
>>>>> With !CONFIG_HIGHMEM, pages are contiguous so use the range clearing
>>>>> primitive clear_user_pages().
>>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>>> ---
>>>>>     include/linux/highmem.h | 18 ++++++++++++++++++
>>>>>     1 file changed, 18 insertions(+)
>>>>> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
>>>>> index 6234f316468c..ed609987e24d 100644
>>>>> --- a/include/linux/highmem.h
>>>>> +++ b/include/linux/highmem.h
>>>>> @@ -207,6 +207,24 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
>>>>>     }
>>>>>     #endif
>>>>>     +#ifndef clear_user_highpages
>>>>
>>>> Maybe we can add a simple kernel doc that points at the doc of clear_user_pages,
>>>> but makes it clear that this for pages that might reside in highmem.
>>> Didn't add one because clear_user_highpage() didn't have one. Will add
>>> for both.
>>>
>>
>> Doesn't have to be excessive. But even I have to keep reminding myself when to
>> use clear_page(), clear_user_page(), clear_user_highpage() ...
> 
> And now all the multi-page variants. Really motivates the removal of
> the HIGHMEM stuff.

:) I'm afraid it will stick around for a couple of years to come.

-- 
Cheers

David / dhildenb

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[David Hildenbrand]

>>> assumes one of the following:
>>>     1. clear_user_highpages is defined by the architecture or,
>>>     2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
>>>     3. !HIGHMEM => arch defines clear_user_pages or clear_user_page
>>> Case 2 is fine, since ARM has clear_user_highpage().
>>> Case 3 runs into a problem since ARM doesn't have clear_user_pages()
>>> or clear_user_page() (it does have the second, but only with !CONFIG_MMU).
>>
>> I think we should look into having a generic fallback version in common code
>> instead for that case, and not require the arch to implement such a loop around
>> clear_user_highpage().
> 
> So, as you suggested, I moved clear_user_pages() to mm/utils.c and
> conditioned it on clear_user_page() also existing.
> 
>    #if defined(clear_user_page) && !defined(clear_user_pages)
>    void clear_user_pages(void *addr, unsigned long vaddr, struct page *page,
>                          unsigned int npages) {
>                        ...
>    }
>    #endif
> 
> That fixed this issue as well since there's no more bogus reference to
> clear_user_page().

I'll have to see the resulting code to comment on details, but if we can handle it in
common code, all good.

> 
> Are there cases in which (TRANSPARENT_HUGEPAGE || HUGETLB) might be enabled
> on ARM?

Arm has

arch/arm/Kconfig:       select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARM_LPAE

and supports hugetlb. So yes on both.

-- 
Cheers

David / dhildenb

Re: [PATCH v7 00/16] mm: folio_zero_user: clear contiguous pages

[Ankur Arora]

Raghavendra K T <raghavendra.kt@amd.com> writes:

> On 9/17/2025 8:54 PM, Ankur Arora wrote:
>> This series adds clearing of contiguous page ranges for hugepages,
>> improving on the current page-at-a-time approach in two ways:
>>
>>   - amortizes the per-page setup cost over a larger extent
>>
>>   - when using string instructions, exposes the real region size
>>     to the processor.
>>
>> A processor could use a knowledge of the extent to optimize the
>> clearing. AMD Zen uarchs, as an example, elide allocation of
>> cachelines for regions larger than L3-size.
> [...]
>
> Hello,
>
> Feel free to add
>
> Tested-by: Raghavendra K T <raghavendra.kt@amd.com>

Great. Thanks Raghu.

> for whole series.
>
> [ I do understand that there may be minor tweeks to clear page patches
> to convert nth_page once David's changes are in]

Yeah and a few other changes based on Andrew and David's comments.

> SUT: AMD Zen5
>
> I also did a quick hack to unconditionally use CLZERO/MOVNT on top of
> Ankur's series to test how much additional benefits can architectural
> enhancements bring in. [ Inline with second part of Ankur's old series before
> preempt lazy changes ]. Please note that it is only for testing ideally
> for lower sizes we would want rep stosb only. and threshold at which
> we need to do non-temporal copy should be a function of L3 and / OR L2 size
> perhaps.
>
> Results:
> base      : 6.17-rc6 + perf bench patches
> clearpage : 6.17-rc6 + whole series from Ankur
> clzero    : 6.17-rc6 + Ankur's series +  clzero (below patch)
> movnt     : 6.17-rc6 + Ankur's series +  movnt (below patch)
>
> Command run: ./perf bench mem mmap -p 2MB -f demand -s 64GB -l 10
>
> Higher = better
>
>                    preempt = lazy (GB/sec)  preempt = voluntary (GB/sec)
>
> base               20.655559                19.712500
> clearpage          35.060572                34.533414
> clzero             66.948422                66.067265
> movnt              51.593506                51.403765

The CLZERO number with page-size=2MB is pretty impressive. But as you
said that non temporal instructions need more thinking related to
thresholds etc.

> CLZERO/MOVNT experimental patch. Hope I have not missed anything here :)

Looks good to me :).

> -- >8 --
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 52c8910ba2ef..26cef2b187b9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -3170,6 +3170,8 @@ config HAVE_ATOMIC_IOMAP
>  	def_bool y
>  	depends on X86_32
>
> +source "arch/x86/Kconfig.cpy"
> +
>  source "arch/x86/kvm/Kconfig"
>
>  source "arch/x86/Kconfig.cpufeatures"
> diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> index 2361066d175e..aa2e62bbfa62 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -84,11 +84,23 @@ static inline void clear_pages(void *addr, unsigned int npages)
>  	 */
>  	kmsan_unpoison_memory(addr, len);
>  	asm volatile(ALTERNATIVE_2("call memzero_page_aligned_unrolled",
> -				   "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
> -				   "rep stosb", X86_FEATURE_ERMS)
> -			: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
> -			: "a" (0)
> -			: "cc", "memory");
> +				"shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD,
> +#if defined(CONFIG_CLEARPAGE_CLZERO)
> +		"call clear_pages_clzero", X86_FEATURE_CLZERO)
> +		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
> +		: "a" (0)
> +		: "cc", "memory");
> +#elif defined(CONFIG_CLEARPAGE_MOVNT)
> +		"call clear_pages_movnt", X86_FEATURE_XMM2)
> +		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
> +		: "a" (0)
> +		: "cc", "memory");
> +#else
> +		"rep stosb", X86_FEATURE_ERMS)
> +		: "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
> +		: "a" (0)
> +		: "cc", "memory");
> +#endif
>  }
>  #define clear_pages clear_pages
>
> diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
> index 27debe0c018c..0848287446dd 100644
> --- a/arch/x86/lib/clear_page_64.S
> +++ b/arch/x86/lib/clear_page_64.S
> @@ -4,6 +4,7 @@
>  #include <linux/cfi_types.h>
>  #include <linux/objtool.h>
>  #include <asm/asm.h>
> +#include <asm/page_types.h>
>
>  /*
>   * Zero page aligned region.
> @@ -119,3 +120,40 @@ SYM_FUNC_START(rep_stos_alternative)
>  	_ASM_EXTABLE_UA(17b, .Lclear_user_tail)
>  SYM_FUNC_END(rep_stos_alternative)
>  EXPORT_SYMBOL(rep_stos_alternative)
> +
> +SYM_FUNC_START(clear_pages_movnt)
> +	.p2align 4
> +.Lstart:
> +	movnti  %rax, 0x00(%rdi)
> +	movnti  %rax, 0x08(%rdi)
> +	movnti  %rax, 0x10(%rdi)
> +	movnti  %rax, 0x18(%rdi)
> +	movnti  %rax, 0x20(%rdi)
> +	movnti  %rax, 0x28(%rdi)
> +	movnti  %rax, 0x30(%rdi)
> +	movnti  %rax, 0x38(%rdi)
> +	addq    $0x40, %rdi
> +	subl    $0x40, %ecx
> +	ja      .Lstart
> +	RET
> +SYM_FUNC_END(clear_pages_movnt)
> +EXPORT_SYMBOL_GPL(clear_pages_movnt)
> +
> +/*
> + * Zero a page using clzero (On AMD, with CPU_FEATURE_CLZERO.)
> + *
> + * Caller needs to issue a sfence at the end.
> + */
> +
> +SYM_FUNC_START(clear_pages_clzero)
> +	movq	%rdi,%rax
> +	.p2align 4
> +.Liter:
> +	clzero
> +	addq    $0x40, %rax
> +	subl    $0x40, %ecx
> +	ja      .Liter
> +	sfence
> +	RET
> +SYM_FUNC_END(clear_pages_clzero)
> +EXPORT_SYMBOL_GPL(clear_pages_clzero)


--
ankur

Re: [PATCH v7 13/16] mm: memory: support clearing page ranges

[Ankur Arora]

Raghavendra K T <rkodsara@amd.com> writes:

> On 9/18/2025 3:14 AM, Andrew Morton wrote:
>> On Wed, 17 Sep 2025 08:24:15 -0700 Ankur Arora <ankur.a.arora@oracle.com> wrote:
>>
>>> Change folio_zero_user() to clear contiguous page ranges instead of
>>> clearing using the current page-at-a-time approach. Exposing the largest
>>> feasible length can be useful in enabling processors to optimize based
>>> on extent.
>> This patch is something which MM developers might care to take a closer
>> look at.
>>
>>> However, clearing in large chunks can have two problems:
>>>
>>>   - cache locality when clearing small folios (< MAX_ORDER_NR_PAGES)
>>>     (larger folios don't have any expectation of cache locality).
>>>
>>>   - preemption latency when clearing large folios.
>>>
>>> Handle the first by splitting the clearing in three parts: the
>>> faulting page and its immediate locality, its left and right
>>> regions; with the local neighbourhood cleared last.
>> Has this optimization been shown to be beneficial?
>> If so, are you able to share some measurements?
>> If not, maybe it should be removed?
>>
>
> I reverted the effect of this patch by hard coding
>
> #define PAGE_CONTIG_NR 1
>
> I see that benefit for voluntary kernel is lost without this change
>
> (for rep stosb)
>
> with PAGE_CONTIG_NR equivalent to 8MB
>
> Preempt mode: voluntary
>
> # Running 'mem/mmap' benchmark:
> # function 'demand' (Demand loaded mmap())
> # Copying 64GB bytes ...
>
>       34.533414 GB/sec
>
>
> with PAGE_CONTIG_NR equivalent to 4KB
>
> # Running 'mem/mmap' benchmark:
> # function 'demand' (Demand loaded mmap())
> # Copying 64GB bytes ...
>
>       20.766059 GB/sec
>
> For now (barring David's recommendations),
> feel free to add
>
> Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>

Thanks Raghu.

--
ankur

Re: [PATCH v7 12/16] arm: mm: define clear_user_highpages()

[Ankur Arora]

David Hildenbrand <david@redhat.com> writes:

>>>> assumes one of the following:
>>>>     1. clear_user_highpages is defined by the architecture or,
>>>>     2. HIGHMEM => arch defines clear_user_highpage or clear_user_page
>>>>     3. !HIGHMEM => arch defines clear_user_pages or clear_user_page
>>>> Case 2 is fine, since ARM has clear_user_highpage().
>>>> Case 3 runs into a problem since ARM doesn't have clear_user_pages()
>>>> or clear_user_page() (it does have the second, but only with !CONFIG_MMU).
>>>
>>> I think we should look into having a generic fallback version in common code
>>> instead for that case, and not require the arch to implement such a loop around
>>> clear_user_highpage().
>> So, as you suggested, I moved clear_user_pages() to mm/utils.c and
>> conditioned it on clear_user_page() also existing.
>>    #if defined(clear_user_page) && !defined(clear_user_pages)
>>    void clear_user_pages(void *addr, unsigned long vaddr, struct page *page,
>>                          unsigned int npages) {
>>                        ...
>>    }
>>    #endif
>> That fixed this issue as well since there's no more bogus reference to
>> clear_user_page().
>
> I'll have to see the resulting code to comment on details, but if we can handle it in
> common code, all good.
>
>> Are there cases in which (TRANSPARENT_HUGEPAGE || HUGETLB) might be enabled
>> on ARM?
>
> Arm has
>
> arch/arm/Kconfig:       select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARM_LPAE
>
> and supports hugetlb. So yes on both.

I tried to figure out a way forward for arm with THP/HUGETLB and AFAICS
the cleanest approach would be to have some version of this patch.

Just to reiterate the problem with arch/arm: it defines
clear_user_highpage(), but does not define clear_user_page().

This means that common code cannot usefully define clear_user_pages().

And the common definition of clear_user_highpages() either needs to use:

  - for HIGHMEM, clear_user_highpage()
  - for !HIGHMEM, clear_user_pages()

The first works but I don't see how to make the second work without adding
some such special handling:

     static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
     					unsigned int npages)
vaddr, page, npages);
     		return;
     	}
     #endif

     	do {
     		clear_user_highpage(page, vaddr);
     		vaddr += PAGE_SIZE;
     		page++;
     	} while (--npages);
     }

(Even this is a bit contorted, as common code shouldn't really need to
have an associated #define for clear_user_pages().)

Thanks

--
ankur

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[David Hildenbrand]

On 25.09.25 07:25, Ankur Arora wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 23.09.25 22:26, Ankur Arora wrote:
>>> David Hildenbrand <david@redhat.com> writes:
>>>
>>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>>> Define fallback versions of clear_pages(), clear_user_pages().
>>>>> In absence of architectural primitives, we just clear pages
>>>>> sequentially.
>>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>>> ---
>>>>>     include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>>>     1 file changed, 38 insertions(+)
>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>>>>> --- a/include/linux/mm.h
>>>>> +++ b/include/linux/mm.h
>>>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>>>>     				unsigned int order) {}
>>>>>     #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>>>>     +#ifndef clear_pages
>>>>> +/**
>>>>> + * clear_pages() - clear a page range using a kernel virtual address.
>>>>
>>>> I'd just call this "clear a page range for kernel-internal use"
>>>>
>>>>> + * @addr: start address
>>>>> + * @npages: number of pages
>>>>> + *
>>>>> + * Assumes that (@addr, +@npages) references a kernel region.
>>>>
>>>> And say here simply that "Use clear_user_pages() instead for clearing a page
>>>> range to be mapped to user space".
>>> So, comments that actually speak to the use instead of technically
>>> correct but unhelpful generalities :). Thanks, good lesson.
>>>
>>>>> + * Does absolutely no exception handling.
>>>>> + */
>>>>> +static inline void clear_pages(void *addr, unsigned int npages)
>>>>> +{
>>>>> +	do {
>>>>> +		clear_page(addr);
>>>>> +		addr += PAGE_SIZE;
>>>>> +	} while (--npages);
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +#ifndef clear_user_pages
>>>>> +/**
>>>>> + * clear_user_pages() - clear a page range mapped by the user.
>>>>
>>>> I'd call this then "clear a page range to be mapped to user space"
>>>>
>>>> Because it's usually called before we actually map it and it will properly flush
>>>> the dcache if required.
>>> Makes sense.
>>>
>>>>> + * @addr: kernel mapped address
>>>>
>>>> "start address"
>>>>
>>>>> + * @vaddr: user mapped address
>>>>
>>>> "start address of the user mapping" ?
>>>>
>>>>> + * @pg: start page
>>>>
>>>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
>>>> thingy, but let's do it better here.
>>>>
>>>>> + * @npages: number of pages
>>>>> + *
>>>>> + * Assumes that the region (@addr, +@npages) has been validated
>>>>> + * already so this does no exception handling.
>>>>> + */
>>>>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>>>>> +do {							\
>>>>> +	clear_user_page(addr, vaddr, pg);		\
>>>>> +	addr += PAGE_SIZE;				\
>>>>> +	vaddr += PAGE_SIZE;				\
>>>>> +	pg++;						\
>>>>> +} while (--npages)
>>>>> +#endif
>>>>
>>>> Should indent with one tab.
>>> Will do. Also acking to the ones above.
>>>
>>>> Any reason this is not a static inline function?
>>> Alas yes. Most architecture code defines clear_user_page() as a macro
>>> where, if they need a to flush the dcache or otherwise do something
>>> special, they need access to some external primitive. And this primitive
>>> which might not be visible in contexts that we include this header.
>>> For instance this one on sparc:
>>>     https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/
>>> Defining as a macro to get around that. But maybe there's a better
>>> way?
>>
>> Can we just move it to mm/utils.c and not have it be an inline function?
> 
> Thanks. Yeah, that's a good place for it.

So, I'm looking into this and I think we should fixup the arch if possible.

I now have

commit 0f90e18abec6b6080af9ee5583cbba28d483a87d (HEAD)
Author: David Hildenbrand <david@redhat.com>
Date:   Fri Oct 10 06:09:51 2025 -0400

     treewide: provide a generic clear_user_page() variant

     Let's drop all variants that effectively map to clear_page() and
     provide it in a generic variant instead.

     We'll use __HAVE_ARCH_CLEAR_USER_PAGE, similar to
     __HAVE_ARCH_COPY_USER_HIGHPAGE, to indicate whether an architecture
     provides it's own variant.

     Maybe at some point these should be CONFIG_ options.

     Signed-off-by: David Hildenbrand <david@redhat.com>


To get started. Did you only run into the issue with sparc or was there 
another one problematic?

-- 
Cheers

David / dhildenb

Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages()

[David Hildenbrand]

On 10.10.25 12:37, David Hildenbrand wrote:
> On 25.09.25 07:25, Ankur Arora wrote:
>>
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> On 23.09.25 22:26, Ankur Arora wrote:
>>>> David Hildenbrand <david@redhat.com> writes:
>>>>
>>>>> On 17.09.25 17:24, Ankur Arora wrote:
>>>>>> Define fallback versions of clear_pages(), clear_user_pages().
>>>>>> In absence of architectural primitives, we just clear pages
>>>>>> sequentially.
>>>>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>>>>> ---
>>>>>>      include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>>>>      1 file changed, 38 insertions(+)
>>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>>> index 1ae97a0b8ec7..0cde9b01da5e 100644
>>>>>> --- a/include/linux/mm.h
>>>>>> +++ b/include/linux/mm.h
>>>>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>>>>>>      				unsigned int order) {}
>>>>>>      #endif	/* CONFIG_DEBUG_PAGEALLOC */
>>>>>>      +#ifndef clear_pages
>>>>>> +/**
>>>>>> + * clear_pages() - clear a page range using a kernel virtual address.
>>>>>
>>>>> I'd just call this "clear a page range for kernel-internal use"
>>>>>
>>>>>> + * @addr: start address
>>>>>> + * @npages: number of pages
>>>>>> + *
>>>>>> + * Assumes that (@addr, +@npages) references a kernel region.
>>>>>
>>>>> And say here simply that "Use clear_user_pages() instead for clearing a page
>>>>> range to be mapped to user space".
>>>> So, comments that actually speak to the use instead of technically
>>>> correct but unhelpful generalities :). Thanks, good lesson.
>>>>
>>>>>> + * Does absolutely no exception handling.
>>>>>> + */
>>>>>> +static inline void clear_pages(void *addr, unsigned int npages)
>>>>>> +{
>>>>>> +	do {
>>>>>> +		clear_page(addr);
>>>>>> +		addr += PAGE_SIZE;
>>>>>> +	} while (--npages);
>>>>>> +}
>>>>>> +#endif
>>>>>> +
>>>>>> +#ifndef clear_user_pages
>>>>>> +/**
>>>>>> + * clear_user_pages() - clear a page range mapped by the user.
>>>>>
>>>>> I'd call this then "clear a page range to be mapped to user space"
>>>>>
>>>>> Because it's usually called before we actually map it and it will properly flush
>>>>> the dcache if required.
>>>> Makes sense.
>>>>
>>>>>> + * @addr: kernel mapped address
>>>>>
>>>>> "start address"
>>>>>
>>>>>> + * @vaddr: user mapped address
>>>>>
>>>>> "start address of the user mapping" ?
>>>>>
>>>>>> + * @pg: start page
>>>>>
>>>>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg
>>>>> thingy, but let's do it better here.
>>>>>
>>>>>> + * @npages: number of pages
>>>>>> + *
>>>>>> + * Assumes that the region (@addr, +@npages) has been validated
>>>>>> + * already so this does no exception handling.
>>>>>> + */
>>>>>> +#define clear_user_pages(addr, vaddr, pg, npages)	\
>>>>>> +do {							\
>>>>>> +	clear_user_page(addr, vaddr, pg);		\
>>>>>> +	addr += PAGE_SIZE;				\
>>>>>> +	vaddr += PAGE_SIZE;				\
>>>>>> +	pg++;						\
>>>>>> +} while (--npages)
>>>>>> +#endif
>>>>>
>>>>> Should indent with one tab.
>>>> Will do. Also acking to the ones above.
>>>>
>>>>> Any reason this is not a static inline function?
>>>> Alas yes. Most architecture code defines clear_user_page() as a macro
>>>> where, if they need a to flush the dcache or otherwise do something
>>>> special, they need access to some external primitive. And this primitive
>>>> which might not be visible in contexts that we include this header.
>>>> For instance this one on sparc:
>>>>      https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/
>>>> Defining as a macro to get around that. But maybe there's a better
>>>> way?
>>>
>>> Can we just move it to mm/utils.c and not have it be an inline function?
>>
>> Thanks. Yeah, that's a good place for it.
> 
> So, I'm looking into this and I think we should fixup the arch if possible.
> 
> I now have
> 
> commit 0f90e18abec6b6080af9ee5583cbba28d483a87d (HEAD)
> Author: David Hildenbrand <david@redhat.com>
> Date:   Fri Oct 10 06:09:51 2025 -0400
> 
>       treewide: provide a generic clear_user_page() variant
> 
>       Let's drop all variants that effectively map to clear_page() and
>       provide it in a generic variant instead.
> 
>       We'll use __HAVE_ARCH_CLEAR_USER_PAGE, similar to
>       __HAVE_ARCH_COPY_USER_HIGHPAGE, to indicate whether an architecture
>       provides it's own variant.
> 
>       Maybe at some point these should be CONFIG_ options.
> 
>       Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> 
> To get started. Did you only run into the issue with sparc or was there
> another one problematic?
> 

Okay, m68k is nasty as well. Change of plans, let's keep a 
clear_user_pages() variant in mm/utils.c when the arch has special 
clear_user_page() needs.

-- 
Cheers

David / dhildenb