On 06.06.24 22:36, Pankaj Raghav (Samsung) wrote:

From: Pankaj Raghav p.raghav@samsung.com

create_pagecache_thp_and_fd() in split_huge_page_test.c used the variable dummy to perform mmap read.

However, this test was skipped even on XFS which has large folio support. The issue was compiler (gcc 13.2.0) was optimizing out the dummy variable, therefore, not creating huge page in the page cache.

Use asm volatile() trick to force the compiler not to optimize out the loop where we read from the mmaped addr. This is similar to what is being done in other tests (cow.c, etc)

As the variable is now used in the asm statement, remove the unused attribute.

Signed-off-by: Pankaj Raghav p.raghav@samsung.com

Changes since v2:

• Use the asm volatile trick to force the compiler to not optimize the read into dummy variable. (David)

  tools/testing/selftests/mm/split_huge_page_test.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c index d3c7f5fb3e7b..e5e8dafc9d94 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -300,7 +300,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, char **addr) { size_t i;

• int __attribute__((unused)) dummy = 0;

• int dummy = 0;

srand(time(NULL)); @@ -341,6 +341,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, for (size_t i = 0; i < fd_size; i++) dummy += *(*addr + i);

• asm volatile("" : "+r" (dummy));

if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) { ksft_print_msg("No large pagecache folio generated, please provide a filesystem supporting large folio\n");

base-commit: d97496ca23a2d4ee80b7302849404859d9058bcd

Acked-by: David Hildenbrand david@redhat.com

I was wondering if we should factor that out into a mm-selftest helper function, but that can be done later.