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

Petr Vorel
2023-11-28T07:46:45Z

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>

> 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},

(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.

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.

> +
> 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