On 06.06.24 22:18, Pankaj Raghav (Samsung) wrote:
On Thu, Jun 06, 2024 at 05:57:21PM +0200, David Hildenbrand wrote:
On 06.06.24 17:56, David Hildenbrand wrote:
On 06.06.24 15:58, Pankaj Raghav (Samsung) wrote:
From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
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.
Add volatile keyword to force compiler not to optimize out the loop
where we read from the mmaped addr.
Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
tools/testing/selftests/mm/split_huge_page_test.c | 2 +-
1 file changed, 1 insertion(+), 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..c573a58f80ab 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;
+ volatile int __attribute__((unused)) dummy = 0;
srand(time(NULL));
base-commit: d97496ca23a2d4ee80b7302849404859d9058bcd
The rick we do in some other tests is:
char *tmp;
tmp = *whatever;
asm volatile("" : "+r" (tmp));
char tmp; of course. See cow.c as an example.
Thanks David! I remember also seeing this when I grepped for volatile in
the selftests directory.
Willy gave the idea of making it as a global variable [1]. But your
trick also works :)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index d3c7f5fb3e7b..9c957703c1f7 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -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");
I am fine with either solutions. But using the trick asm volatile is more
cleaner than making it a global variable IMO and makes it more uniform
across the other mm tests.
You can then even the "__attribute__((unused))", because the compile
must assume that it is used inside the asm statement.
--
Cheers,
David / dhildenb
