[PATCH v2 6/6] alloc_tag: config to store page allocation tag refs in page flags

Suren Baghdasaryan
2024-09-02T04:41:45Z

Add CONFIG_PGALLOC_TAG_USE_PAGEFLAGS to store allocation tag
references directly in the page flags. This removes dependency on
page_ext and results in better performance for page allocations as
well as reduced page_ext memory overhead.
CONFIG_PGALLOC_TAG_REF_BITS controls the number of bits required
to be available in the page flags to store the references. If the
number of page flag bits is insufficient, the build will fail and
either CONFIG_PGALLOC_TAG_REF_BITS would have to be lowered or
CONFIG_PGALLOC_TAG_USE_PAGEFLAGS should be disabled.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/mmzone.h | 3 ++
include/linux/page-flags-layout.h | 10 +++++--
include/linux/pgalloc_tag.h | 48 +++++++++++++++++++++++++++++++
lib/Kconfig.debug | 27 +++++++++++++++--
lib/alloc_tag.c | 4 +++
mm/page_ext.c | 2 +-
6 files changed, 89 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 17506e4a2835..0dd2b42f7cb6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1085,6 +1085,7 @@ static inline bool zone_is_empty(struct zone *zone)
#define KASAN_TAG_PGOFF (LAST_CPUPID_PGOFF - KASAN_TAG_WIDTH)
#define LRU_GEN_PGOFF (KASAN_TAG_PGOFF - LRU_GEN_WIDTH)
#define LRU_REFS_PGOFF (LRU_GEN_PGOFF - LRU_REFS_WIDTH)
+#define ALLOC_TAG_REF_PGOFF (LRU_REFS_PGOFF - ALLOC_TAG_REF_WIDTH)

/*
* Define the bit shifts to access each section. For non-existent
@@ -1096,6 +1097,7 @@ static inline bool zone_is_empty(struct zone *zone)
#define ZONES_PGSHIFT (ZONES_PGOFF * (ZONES_WIDTH != 0))
#define LAST_CPUPID_PGSHIFT (LAST_CPUPID_PGOFF * (LAST_CPUPID_WIDTH != 0))
#define KASAN_TAG_PGSHIFT (KASAN_TAG_PGOFF * (KASAN_TAG_WIDTH != 0))
+#define ALLOC_TAG_REF_PGSHIFT (ALLOC_TAG_REF_PGOFF * (ALLOC_TAG_REF_WIDTH != 0))

/* NODE:ZONE or SECTION:ZONE is used to ID a zone for the buddy allocator */
#ifdef NODE_NOT_IN_PAGE_FLAGS
@@ -1116,6 +1118,7 @@ static inline bool zone_is_empty(struct zone *zone)
#define LAST_CPUPID_MASK ((1UL << LAST_CPUPID_SHIFT) - 1)
#define KASAN_TAG_MASK ((1UL << KASAN_TAG_WIDTH) - 1)
#define ZONEID_MASK ((1UL << ZONEID_SHIFT) - 1)
+#define ALLOC_TAG_REF_MASK ((1UL << ALLOC_TAG_REF_WIDTH) - 1)

static inline enum zone_type page_zonenum(const struct page *page)
{
diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
index 7d79818dc065..21bba7c8c965 100644
--- a/include/linux/page-flags-layout.h
+++ b/include/linux/page-flags-layout.h
@@ -5,6 +5,12 @@
#include <linux/numa.h>
#include <generated/bounds.h>

+#ifdef CONFIG_PGALLOC_TAG_USE_PAGEFLAGS
+#define ALLOC_TAG_REF_WIDTH CONFIG_PGALLOC_TAG_REF_BITS
+#else
+#define ALLOC_TAG_REF_WIDTH 0
+#endif
+
/*
* When a memory allocation must conform to specific limitations (such
* as being suitable for DMA) the caller will pass in hints to the
@@ -91,7 +97,7 @@
#endif

#if ZONES_WIDTH + LRU_GEN_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
- KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+ KASAN_TAG_WIDTH + ALLOC_TAG_REF_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
#define LAST_CPUPID_WIDTH LAST_CPUPID_SHIFT
#else
#define LAST_CPUPID_WIDTH 0
@@ -102,7 +108,7 @@
#endif

#if ZONES_WIDTH + LRU_GEN_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
- KASAN_TAG_WIDTH + LAST_CPUPID_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
+ KASAN_TAG_WIDTH + ALLOC_TAG_REF_WIDTH + LAST_CPUPID_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
#error "Not enough bits in page flags"
#endif

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index a7f8f00c118f..dcb6706dee15 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -118,6 +118,52 @@ static inline void write_pgref(pgalloc_tag_ref *pgref, union codetag_ref *ref)
void __init alloc_tag_sec_init(void);

#endif /* PGALLOC_TAG_DIRECT_REF */
+
+#ifdef CONFIG_PGALLOC_TAG_USE_PAGEFLAGS
+
+typedef struct page *pgtag_ref_handle;
+
+/* Should be called only if mem_alloc_profiling_enabled() */
+static inline pgtag_ref_handle get_page_tag_ref(struct page *page,
+ union codetag_ref *ref)
+{
+ if (page) {
+ pgalloc_tag_ref pgref;
+
+ pgref = (page->flags >> ALLOC_TAG_REF_PGSHIFT) & ALLOC_TAG_REF_MASK;
+ read_pgref(&pgref, ref);
+ return page;
+ }
+
+ return NULL;
+}
+
+static inline void put_page_tag_ref(pgtag_ref_handle page)
+{
+ WARN_ON(!page);
+}
+
+static inline void update_page_tag_ref(pgtag_ref_handle page, union codetag_ref *ref)
+{
+ unsigned long old_flags, flags, val;
+ pgalloc_tag_ref pgref;
+
+ if (WARN_ON(!page || !ref))
+ return;
+
+ write_pgref(&pgref, ref);
+ val = (unsigned long)pgref;
+ val = (val & ALLOC_TAG_REF_MASK) << ALLOC_TAG_REF_PGSHIFT;
+ do {
+ old_flags = READ_ONCE(page->flags);
+ flags = old_flags;
+ flags &= ~(ALLOC_TAG_REF_MASK << ALLOC_TAG_REF_PGSHIFT);
+ flags |= val;
+ } while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
+}
+
+#else /* CONFIG_PGALLOC_TAG_USE_PAGEFLAGS */
+
#include <linux/page_ext.h>

extern struct page_ext_operations page_alloc_tagging_ops;
@@ -166,6 +212,8 @@ static inline void update_page_tag_ref(pgtag_ref_handle pgref, union codetag_ref
write_pgref(pgref, ref);
}

+#endif /* CONFIG_PGALLOC_TAG_USE_PAGEFLAGS */
+
static inline void clear_page_tag_ref(struct page *page)
{
if (mem_alloc_profiling_enabled()) {
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 253f9c2028da..9fc8c1981f27 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -979,7 +979,7 @@ config MEM_ALLOC_PROFILING
depends on PROC_FS
depends on !DEBUG_FORCE_WEAK_PER_CPU
select CODE_TAGGING
- select PAGE_EXTENSION
+ select PAGE_EXTENSION if !PGALLOC_TAG_USE_PAGEFLAGS
select SLAB_OBJ_EXT
help
Track allocation source code and record total allocation size
@@ -1000,10 +1000,26 @@ config MEM_ALLOC_PROFILING_DEBUG
Adds warnings with helpful error messages for memory allocation
profiling.

+config PGALLOC_TAG_USE_PAGEFLAGS
+ bool "Use pageflags to encode page allocation tag reference"
+ default n
+ depends on MEM_ALLOC_PROFILING
+ help
+ When set, page allocation tag references are encoded inside page
+ flags, otherwise they are encoded in page extensions.
+
+ Setting this flag reduces memory and performance overhead of memory
+ allocation profiling but also limits how many allocations can be
+ tagged. The number of bits is set by PGALLOC_TAG_USE_PAGEFLAGS and
+ they must fit in the page flags field.
+
+ Say N if unsure.
+
config PGALLOC_TAG_REF_BITS
int "Number of bits for page allocation tag reference (10-64)"
range 10 64
- default "64"
+ default "16" if PGALLOC_TAG_USE_PAGEFLAGS
+ default "64" if !PGALLOC_TAG_USE_PAGEFLAGS
depends on MEM_ALLOC_PROFILING
help
Number of bits used to encode a page allocation tag reference.
@@ -1011,6 +1027,13 @@ config PGALLOC_TAG_REF_BITS
Smaller number results in less memory overhead but limits the number of
allocations which can be tagged (including allocations from modules).

+ If PGALLOC_TAG_USE_PAGEFLAGS is set, the number of requested bits should
+ fit inside the page flags.
+
+ If PGALLOC_TAG_USE_PAGEFLAGS is not set, the number of bits used to store
+ a reference is rounded up to the closest basic type. If set higher than 32,
+ a direct pointer to the allocation tag is stored for performance reasons.
+
source "lib/Kconfig.kasan"
source "lib/Kconfig.kfence"
source "lib/Kconfig.kmsan"
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 73791aa55ab6..34820650186d 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -476,6 +476,8 @@ static int __init setup_early_mem_profiling(char *str)
}
early_param("sysctl.vm.mem_profiling", setup_early_mem_profiling);

+#ifndef CONFIG_PGALLOC_TAG_USE_PAGEFLAGS
+
static __init bool need_page_alloc_tagging(void)
{
return mem_profiling_support;
@@ -492,6 +494,8 @@ struct page_ext_operations page_alloc_tagging_ops = {
};
EXPORT_SYMBOL(page_alloc_tagging_ops);

+#endif /* CONFIG_PGALLOC_TAG_USE_PAGEFLAGS */
+
#ifdef CONFIG_SYSCTL
static struct ctl_table memory_allocation_profiling_sysctls[] = {
{
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 641d93f6af4c..5f993c271ee7 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -83,7 +83,7 @@ static struct page_ext_operations *page_ext_ops[] __initdata = {
#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
&page_idle_ops,
#endif
-#ifdef CONFIG_MEM_ALLOC_PROFILING
+#if defined(CONFIG_MEM_ALLOC_PROFILING) && !defined(CONFIG_PGALLOC_TAG_USE_PAGEFLAGS)
&page_alloc_tagging_ops,
#endif
#ifdef CONFIG_PAGE_TABLE_CHECK
--
2.46.0.469.g59c65b2a67-goog