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

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

[Pengfei Xu]

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.
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.

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


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

[Li Wang]

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.


> 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.

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

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

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

[Li Wang]

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.
>
>
>> 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.
>
> 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

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

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

[Pengfei Xu]

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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