mm: selftest to verify zero-filled pages are mapped to zeropage

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@gmail.com
Signed-off-by: Alexander Zhu <alexlzhu@fb.com>
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Acked-by: Rik van Riel <riel@surriel.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: Kairui Song <ryncsn@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
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>
Cc: Shuang Zhai <szhai2@cs.rochester.edu>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index e5e8dafc9d942b9fd58abd02192fa04fc229eb22..eb6d1b9fc3625fdbd71ef3bf2c9e4970ab51a7b4 100644 (file)
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -84,6 +84,76 @@ static void write_debugfs(const char *fmt, ...)
        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();

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 5a62530da3b563b38164fb9491bcc996cd323e33..d8d0cf04bb57fd22bd7748fffec6a23c3103e35c 100644 (file)
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/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)
 {

diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 9007c420d52c5201c40284f4f91cd7687f9d7188..2eaed82099255e09ffd38ad9714994397f304685 100644 (file)
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -39,6 +39,7 @@ unsigned long pagemap_get_pfn(int fd, char *start);
 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);