Re: [LTP] [PATCH v1] mem: disable KSM smart scan for ksm tests

Stefan Roesch
2023-12-01T20:06:32Z

Petr Vorel <pvorel@suse.cz> writes:

> Hi Stefan,
>
>> This disables the "smart scan" KSM feature to make sure that the volatile
>> count remains at 0.
>
>> Signed-off-by: Stefan Roesch <devkernel.io>
> nit: you forgot 'shr@'
> Signed-off-by: Stefan Roesch <shr@devkernel.io>
>

Thanks, will be fixed with the next version.

>> Reported-by: kernel test robot <oliver.sang@intel.com>
>> Closes: https://lore.kernel.org/oe-lkp/202311161132.13d8ce5a-oliver.sang@intel.com
>> ---
>> testcases/kernel/mem/lib/mem.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>
>> diff --git a/testcases/kernel/mem/lib/mem.c b/testcases/kernel/mem/lib/mem.c
>> index fbfeef026..ef274a3ac 100644
>> --- a/testcases/kernel/mem/lib/mem.c
>> +++ b/testcases/kernel/mem/lib/mem.c
>> @@ -454,6 +454,9 @@ void create_same_memory(int size, int num, int unit)
>> {'a', size*MB}, {'a', size*MB}, {'d', size*MB}, {'d', size*MB},
>> };
>
>> + /* Disable smart scan for correct volatile counts. */
>> + SAFE_FILE_PRINTF(PATH_KSM "smart_scan", "0");
> NOTE, this fails on the systems without /sys/kernel/mm/ksm/smart_scan:
>
> mem.c:458: TBROK: Failed to open FILE '/sys/kernel/mm/ksm/smart_scan' for writing: EACCES (13)
>
> NOTE, we normally handle the setup like this in test setup function.
>
> But new API has .save_restore which is more robust for tasks like this.
> It's already used in ksm01.c, you need just to add this line:
> {"/sys/kernel/mm/ksm/smart_scan", "0", TST_SR_SKIP},
>

I'll add it with the next version

> (instead of both SAFE_FILE_PRINTF)
>
> See:
> https://github.com/linux-test-project/ltp/wiki/C-Test-API#127-saving--restoring-procsys-values
>
> I wonder if ksm01.c is the only ksm test which needs to disable this.
>

Other tests will also need it. They also use the create_same_memory()
function.

> also nit: there is a wrong indent (spaces instead of tabs), please be consistent
> with the file content.
>
> NOTE: while this fixes problem on 6.7.0-rc1-2.g86e46c2-default (openSUSE),
> it does not fixes other problem on 6.5.10 on Debian (16 errors like these below):
>
> mem.c:252: TFAIL: pages_shared is not 2 but 5038.
> mem.c:252: TFAIL: pages_sharing is not 98302 but 593629.
> mem.c:252: TFAIL: pages_volatile is not 0 but 391.
> mem.c:252: TFAIL: pages_unshared is not 0 but 149157.
>
> I have no idea if this is a real bug which needs to be fixed or test false
> positive to be fixed, or whether the problem has already been fixed in newer
> kernels.
>

This is a different problem. "Smart scan was introduced with 6.7"

>> +
>> ps = sysconf(_SC_PAGE_SIZE);
>> pages = MB / ps;
>
>> @@ -526,6 +529,7 @@ void create_same_memory(int size, int num, int unit)
>
>> tst_res(TINFO, "stop KSM.");
>> SAFE_FILE_PRINTF(PATH_KSM "run", "0");
>> + SAFE_FILE_PRINTF(PATH_KSM "smart_scan", "1");
> nit: Again, wrong indent. You could have seen it also in the generated patch.
>
> Kind regards,
> Petr
>
>> final_group_check(0, 0, 0, 0, 0, 0, size * pages * num);
>
>> while (waitpid(-1, &status, 0) > 0)
>
>> base-commit: 8c89ef3d451087ed6e18750bd5eedd10e5ab3d2e