[LTP] [PATCH] madvise06: Raise the bar for judging failure

[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.

So this patch is aimed at improving the accuracy and clarity of the test results.
Specifically, the use of two separate variables to track the results of different
comparisons will make it easier to understand what the test is doing.

Additionally, the 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.

Finally, the change to the second tst_res call is intended to make the test more
lenient, as it now passes if either no page faults occur or the swap cache size
is larger than expected.

Reported-by: Paul Bunyan <pbunyan@redhat.com>
Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Richard Palethorpe <rpalethorpe@suse.de>
Cc: Yongqiang Liu <liuyongqiang13@huawei.com>
Cc: Eirik Fuller <efuller@redhat.com>
---
 testcases/kernel/syscalls/madvise/madvise06.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/testcases/kernel/syscalls/madvise/madvise06.c b/testcases/kernel/syscalls/madvise/madvise06.c
index c7967ae6f..5bd428bd9 100644
--- a/testcases/kernel/syscalls/madvise/madvise06.c
+++ b/testcases/kernel/syscalls/madvise/madvise06.c
@@ -164,7 +164,7 @@ static int get_page_fault_num(void)
 
 static void test_advice_willneed(void)
 {
-	int loops = 100, res;
+	int loops = 100, res1, res2;
 	char *target;
 	long swapcached_start, swapcached;
 	int page_fault_num_1, page_fault_num_2;
@@ -197,10 +197,10 @@ static void test_advice_willneed(void)
 	} while (swapcached < swapcached_start + PASS_THRESHOLD_KB && loops > 0);
 
 	meminfo_diag("After madvise");
-	res = swapcached > swapcached_start + PASS_THRESHOLD_KB;
-	tst_res(res ? TPASS : TFAIL,
+	res1 = swapcached > swapcached_start + PASS_THRESHOLD_KB;
+	tst_res(res1 ? TPASS : TINFO,
 		"%s than %ld Kb were moved to the swap cache",
-		res ? "more" : "less", PASS_THRESHOLD_KB);
+		res1 ? "more" : "less", PASS_THRESHOLD_KB);
 
 	loops = 100;
 	SAFE_FILE_LINES_SCANF("/proc/meminfo", "SwapCached: %ld", &swapcached_start);
@@ -225,9 +225,9 @@ static void test_advice_willneed(void)
 			page_fault_num_2);
 	meminfo_diag("After page access");
 
-	res = page_fault_num_2 - page_fault_num_1;
-	tst_res(res == 0 ? TPASS : TFAIL,
-		"%d pages were faulted out of 3 max", res);
+	res2 = page_fault_num_2 - page_fault_num_1;
+	tst_res(((res2 == 0) || res1) ? TPASS : TFAIL,
+		"%d pages were faulted out of 3 max", res2);
 
 	SAFE_MUNMAP(target, CHUNK_SZ);
 }
-- 
2.38.1