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
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------------------------------------------------------
From: Alexander Zhu <alexlzhu@xxxxxx>
Subject: mm: selftest to verify zero-filled pages are mapped to zeropage
Date: Fri, 30 Aug 2024 11:03:37 +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/20240830100438.3623486-4-usamaarif642@xxxxxxxxx
Signed-off-by: Alexander Zhu <alexlzhu@xxxxxx>
Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Kairui Song <ryncsn@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Nico Pache <npache@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Shuang Zhai <zhais@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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);
+unsigned long 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@xxxxxx are
mm-selftest-to-verify-zero-filled-pages-are-mapped-to-zeropage.patch
