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

Stefan Roesch
2023-12-01T20:08:06Z

Li Wang <liwang@redhat.com> writes:

> 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?
>

In the next version of the patch I'll add a new test case specifically
to test smart scan.