From ecc1793b2d08efeb2d1795814d2ea350c9d6992b Mon Sep 17 00:00:00 2001 From: Pankaj Raghav Date: Thu, 6 Jun 2024 20:36:19 +0000 Subject: [PATCH] selftests/mm: use asm volatile to not optimize mmap read variable 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. Link: https://lkml.kernel.org/r/20240606203619.677276-1-kernel@pankajraghav.com Signed-off-by: Pankaj Raghav Reviewed-by: Zi Yan Acked-by: David Hildenbrand Cc: Luis Chamberlain Cc: Matthew Wilcox (Oracle) Cc: Pankaj Raghav Cc: Shuah Khan Signed-off-by: Andrew Morton --- 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"); -- 2.50.1