selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"

Patch series "selftests/mm: reuse FORCE_READ to replace "asm volatile("" :
"+r" (XXX));" and some cleanup", v2.

This series introduces a common FORCE_READ() macro to replace the cryptic
asm volatile("" : "+r" (variable)); construct used in several mm
selftests.  This improves code readability and maintainability by removing
duplicated, hard-to-understand code.


This patch (of 2):

Several mm selftests use the `asm volatile("" : "+r" (variable));`
construct to force a read of a variable, preventing the compiler from
optimizing away the memory access.  This idiom is cryptic and duplicated
across multiple test files.

Following a suggestion from David[1], this patch refactors this common
pattern into a FORCE_READ() macro

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/lkml/[email protected]/ [1]
Signed-off-by: wang lian <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Wei Yang <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 3 deletions

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index aa7400ed0e99..6640748ff221 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -398,7 +398,6 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
 		char **addr)
 {
 	size_t i;
-	int dummy = 0;
 	unsigned char buf[1024];
 
 	srand(time(NULL));
@@ -440,8 +439,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
 	madvise(*addr, fd_size, MADV_HUGEPAGE);
 
 	for (size_t i = 0; i < fd_size; i++)
-		dummy += *(*addr + i);
-	asm volatile("" : "+r" (dummy));
+		FORCE_READ((*addr + i));
 
 	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");