Received-SPF: pass (google.com: domain of linux-kernel+bounces-204402-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
From: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
To: Shuah Khan <shuah@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: willy@infradead.org,
	linux-kernel@vger.kernel.org,
	linux-mm@kvack.org,
	kernel@pankajraghav.com,
	gost.dev@samsung.com,
	mcgrof@kernel.org,
	linux-kselftest@vger.kernel.org,
	Zi Yan <zi.yan@sent.com>,
	Pankaj Raghav <p.raghav@samsung.com>
Subject: [PATCH] selftests/mm: use volatile keyword to not optimize mmap read variable
Date: Thu,  6 Jun 2024 13:58:35 +0000
Message-ID: <20240606135835.600022-1-kernel@pankajraghav.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

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.

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@samsung.com>
---
 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
-- 
2.44.1