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

[Li Wang]

Hi Stefan, Petr,

On Tue, Nov 28, 2023 at 3:46 PM Petr Vorel <pvorel@suse.cz> wrote:

> 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},
>

I guess we need to set 'TST_SR_SKIP_MISSING | TST_SR_TBROK_RO'
as the last field. Because TST_SR_SKIP will continue the test without
writing '0' to the smart_scan file, that's not correct if the file exists.
It will
ignore a kernel bug (smart_scan can't be written) by that config.

Per the Doc Petr pointed below:
  TST_SR_SKIP_MISSING – Continue without saving the file if it does not
exist
  TST_SR_TBROK_RO – End test with TBROK if the file is read-only
  TST_SR_SKIP_RO – Continue without saving the file if it is read-only
  TST_SR_SKIP – Equivalent to 'TST_SR_SKIP_MISSING | TST_SR_SKIP_RO'



> (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.
>

I think all of the ksm0*.c tests should disable it by the config. The
smart_scan
will impact all the tests with invoke key function create_same_memory().



>
> 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.
>

It is more like a real bug, the Debain kernel-6.5.10 does not contain
this smart_scan feature. Or you may try to build the latest kernel
on your platform to see if it can be reproduced as well.



>
> > +
> >       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
>
>

One more comment not related to this patch:

@Stefan, do you have a test (or plan to) verify the 'smart_scan' feture
works?
As we do disables it for all ksm* tests in LTP, so, it would be great to
have one
for testing in enable mode. What do you think?

-- 
Regards,
Li Wang