[LTP] [PATCh v2] madvise06: stop throwing failure when MADV_WILLNEED is ignored

[Li Wang]

There is an intermittent failure which we have observed many times whether
on rhel or mainline kernel. But we're unable to stable reproduce it:

    43	madvise06.c:201: TFAIL: less than 102400 Kb were moved to the swap cache
    ...

However it does not look like a kernel issue, because SwapCached change is
not strictly abiding by the principle of MADV_WILLNEED advice. That means it
all depends on the kernel's specific circumstances. The value of the threshold
is debatable at least from my point of view, its use 1/4 is not guaranteed
100% safe.

As MADV_WILLNEED is just advice to the kernel, not a guarantee. The kernel may
choose to ignore the advice, or may prioritize other memory management tasks
over pre-loading the advised pages.

This change to report a test result of "TINFO" instead of "TFAIL" when the swap
cache size is less than expected would be intended to indicate that this is an
acceptable outcome. Same changes apply to the page_fault counting as well.

Reported-by: Paul Bunyan <pbunyan@redhat.com>
Cc: Richard Palethorpe <rpalethorpe@suse.de>
Cc: Yongqiang Liu <liuyongqiang13@huawei.com>
Cc: Eirik Fuller <efuller@redhat.com>
Signed-off-by: Li Wang <liwang@redhat.com>
---
 testcases/kernel/syscalls/madvise/madvise06.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/syscalls/madvise/madvise06.c b/testcases/kernel/syscalls/madvise/madvise06.c
index c7967ae6f..0e5ce3276 100644
--- a/testcases/kernel/syscalls/madvise/madvise06.c
+++ b/testcases/kernel/syscalls/madvise/madvise06.c
@@ -198,7 +198,7 @@ static void test_advice_willneed(void)
 
 	meminfo_diag("After madvise");
 	res = swapcached > swapcached_start + PASS_THRESHOLD_KB;
-	tst_res(res ? TPASS : TFAIL,
+	tst_res(res ? TPASS : TINFO,
 		"%s than %ld Kb were moved to the swap cache",
 		res ? "more" : "less", PASS_THRESHOLD_KB);
 
@@ -226,7 +226,7 @@ static void test_advice_willneed(void)
 	meminfo_diag("After page access");
 
 	res = page_fault_num_2 - page_fault_num_1;
-	tst_res(res == 0 ? TPASS : TFAIL,
+	tst_res(res == 0 ? TPASS : TINFO,
 		"%d pages were faulted out of 3 max", res);
 
 	SAFE_MUNMAP(target, CHUNK_SZ);
-- 
2.38.1