+ mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: selftest to verify zero-filled pages are mapped to zeropage
has been added to the -mm mm-unstable branch.  Its filename is
     mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Alexander Zhu <alexlzhu@fb.com>
Subject: mm: selftest to verify zero-filled pages are mapped to zeropage
Date: Wed, 7 Aug 2024 14:46:48 +0100

When a THP is split, any subpage that is zero-filled will be mapped to the
shared zeropage, hence saving memory.  Add selftest to verify this by
allocating zero-filled THP and comparing RssAnon before and after split.

Link: https://lkml.kernel.org/r/20240807134732.3292797-4-usamaarif642@gmail.com
Signed-off-by: Alexander Zhu <alexlzhu@fb.com>
Acked-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Shuang Zhai <zhais@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/split_huge_page_test.c |   71 ++++++++++++
 tools/testing/selftests/mm/vm_util.c              |   22 +++
 tools/testing/selftests/mm/vm_util.h              |    1 
 3 files changed, 94 insertions(+)

--- a/tools/testing/selftests/mm/split_huge_page_test.c~mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage
+++ a/tools/testing/selftests/mm/split_huge_page_test.c
@@ -84,6 +84,76 @@ static void write_debugfs(const char *fm
 	write_file(SPLIT_DEBUGFS, input, ret + 1);
 }
 
+static char *allocate_zero_filled_hugepage(size_t len)
+{
+	char *result;
+	size_t i;
+
+	result = memalign(pmd_pagesize, len);
+	if (!result) {
+		printf("Fail to allocate memory\n");
+		exit(EXIT_FAILURE);
+	}
+
+	madvise(result, len, MADV_HUGEPAGE);
+
+	for (i = 0; i < len; i++)
+		result[i] = (char)0;
+
+	return result;
+}
+
+static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hpages, size_t len)
+{
+	unsigned long rss_anon_before, rss_anon_after;
+	size_t i;
+
+	if (!check_huge_anon(one_page, 4, pmd_pagesize)) {
+		printf("No THP is allocated\n");
+		exit(EXIT_FAILURE);
+	}
+
+	rss_anon_before = rss_anon();
+	if (!rss_anon_before) {
+		printf("No RssAnon is allocated before split\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* split all THPs */
+	write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
+		      (uint64_t)one_page + len, 0);
+
+	for (i = 0; i < len; i++)
+		if (one_page[i] != (char)0) {
+			printf("%ld byte corrupted\n", i);
+			exit(EXIT_FAILURE);
+		}
+
+	if (!check_huge_anon(one_page, 0, pmd_pagesize)) {
+		printf("Still AnonHugePages not split\n");
+		exit(EXIT_FAILURE);
+	}
+
+	rss_anon_after = rss_anon();
+	if (rss_anon_after >= rss_anon_before) {
+		printf("Incorrect RssAnon value. Before: %ld After: %ld\n",
+		       rss_anon_before, rss_anon_after);
+		exit(EXIT_FAILURE);
+	}
+}
+
+void split_pmd_zero_pages(void)
+{
+	char *one_page;
+	int nr_hpages = 4;
+	size_t len = nr_hpages * pmd_pagesize;
+
+	one_page = allocate_zero_filled_hugepage(len);
+	verify_rss_anon_split_huge_page_all_zeroes(one_page, nr_hpages, len);
+	printf("Split zero filled huge pages successful\n");
+	free(one_page);
+}
+
 void split_pmd_thp(void)
 {
 	char *one_page;
@@ -431,6 +501,7 @@ int main(int argc, char **argv)
 
 	fd_size = 2 * pmd_pagesize;
 
+	split_pmd_zero_pages();
 	split_pmd_thp();
 	split_pte_mapped_thp();
 	split_file_backed_thp();
--- a/tools/testing/selftests/mm/vm_util.c~mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage
+++ a/tools/testing/selftests/mm/vm_util.c
@@ -12,6 +12,7 @@
 
 #define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
 #define SMAP_FILE_PATH "/proc/self/smaps"
+#define STATUS_FILE_PATH "/proc/self/status"
 #define MAX_LINE_LENGTH 500
 
 unsigned int __page_size;
@@ -171,6 +172,27 @@ uint64_t read_pmd_pagesize(void)
 	return strtoul(buf, NULL, 10);
 }
 
+unsigned long rss_anon(void)
+{
+	unsigned long rss_anon = 0;
+	FILE *fp;
+	char buffer[MAX_LINE_LENGTH];
+
+	fp = fopen(STATUS_FILE_PATH, "r");
+	if (!fp)
+		ksft_exit_fail_msg("%s: Failed to open file %s\n", __func__, STATUS_FILE_PATH);
+
+	if (!check_for_pattern(fp, "RssAnon:", buffer, sizeof(buffer)))
+		goto err_out;
+
+	if (sscanf(buffer, "RssAnon:%10lu kB", &rss_anon) != 1)
+		ksft_exit_fail_msg("Reading status error\n");
+
+err_out:
+	fclose(fp);
+	return rss_anon;
+}
+
 bool __check_huge(void *addr, char *pattern, int nr_hpages,
 		  uint64_t hpage_size)
 {
--- a/tools/testing/selftests/mm/vm_util.h~mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage
+++ a/tools/testing/selftests/mm/vm_util.h
@@ -39,6 +39,7 @@ unsigned long pagemap_get_pfn(int fd, ch
 void clear_softdirty(void);
 bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
 uint64_t read_pmd_pagesize(void);
+uint64_t rss_anon(void);
 bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size);
 bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size);
 bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
_

Patches currently in -mm which might be from alexlzhu@fb.com are

mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage.patch