Re: [LTP] [PATCH v1 1/1] migrate_pages03: remove wait_ksmd_full_scan() check because it's not necessary

[Pengfei Xu <pengfei.xu@intel.com>]

Hi Li Wang and Andrea Arcangeli,

On 2024-07-18 at 18:09:56 +0800, Li Wang wrote:
> Sorry, forgot to cc Andrea Arcangeli in the last reply.
> 
> 
> On Thu, Jul 18, 2024 at 6:06 PM Li Wang <liwang@redhat.com> wrote:
> 
> > Pengfei Xu <pengfei.xu@intel.com> wrote:
> >
> > Remove wait_ksmd_full_scan() check because it's not a necessary step for
> >> migrate_pages03 syscall test:
> >> 1. KSM(kernel samepage merging) could be enabled and it is optional for
> >> migrate_pages syscall testing.
> >>
> >
> > The wait_ksmd_full_scan guarantees the actual merging happens then test
> > can migrate those merged KSM pages to reproduce the regression panic in
> > kernel commit 4b0ece6fa0167b.
> >
> > So this is a necessary configuration before testing.

I did not consider the above situation. Is it possible to improve
wait_ksmd_full_scan() to handle the scenario described in point 2?

> >
> >
> >> 2. When server launched any qemu guest, wait_ksmd_full_scan() will in
> >> infinite loop due to /sys/kernel/mm/ksm/full_scans number would not
> >> increase anymore, and migrate_pages03 will failed with timeout reason.
> >> After removed wait_ksmd_full_scan(), migrate_pages03 could pass without
> >> issue.
> >
> >
> > Yes, this timeout problem likely exists. That is the KSM design which can't
> > avoid "unrelated" page merging happening in the background.
> > But removing the wait_ksmd_full_scan might not be a good approach IMHO.

Yes, thanks for above background info sharing!

Best Regards,
Thank you!

> >
> > Cc @Andrea Arcangeli <aarcange@redhat.com> if he has good suggestions on
> > the test.
> >
> >
> >> Signed-off-by: Pengfei Xu <pengfei.xu@intel.com>
> >> ---
> >>  testcases/kernel/syscalls/migrate_pages/migrate_pages03.c | 1 -
> >>  1 file changed, 1 deletion(-)
> >>
> >> diff --git a/testcases/kernel/syscalls/migrate_pages/migrate_pages03.c
> >> b/testcases/kernel/syscalls/migrate_pages/migrate_pages03.c
> >> index 4d3299b61..f514ed10c 100644
> >> --- a/testcases/kernel/syscalls/migrate_pages/migrate_pages03.c
> >> +++ b/testcases/kernel/syscalls/migrate_pages/migrate_pages03.c
> >> @@ -95,7 +95,6 @@ static void setup(void)
> >>
> >>         SAFE_FILE_SCANF(PATH_KSM "run", "%d", &orig_ksm_run);
> >>         SAFE_FILE_PRINTF(PATH_KSM "run", "%d", 1);
> >> -       wait_ksmd_full_scan();
> >>  }
> >>
> >>  static void cleanup(void)
> >> --
> >> 2.43.0
> >>
> >>
> >> --
> >> Mailing list info: https://lists.linux.it/listinfo/ltp
> >>
> >>
> >
> > --
> > Regards,
> > Li Wang
> >
> 
> 
> -- 
> Regards,
> Li Wang

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