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

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

[Stefan Roesch]

This disables the "smart scan" KSM feature to make sure that the volatile
count remains at 0.

Signed-off-by: Stefan Roesch <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");
+
 	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");
 	final_group_check(0, 0, 0, 0, 0, 0, size * pages * num);
 
 	while (waitpid(-1, &status, 0) > 0)

base-commit: 8c89ef3d451087ed6e18750bd5eedd10e5ab3d2e
-- 
2.39.3

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

[Petr Vorel]

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

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

[Li Wang]

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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

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

[Petr Vorel]

Hi Stefan, Li,

> 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().

ksm05.c and ksm06.c does not use create_same_memory(). Or did I overlook
something?

> > 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.


I'll try to reproduce this on mainline kernel 6.5, 6.6 and 6.7.


> > > +
> > >       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?

This makes perfect sense even if I'm not that ksm05.c and ksm06.c also needs to
disable smart_scan.

Kind regards,
Petr

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

[Li Wang]

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On Wed, Nov 29, 2023 at 12:51 AM Petr Vorel <pvorel@suse.cz> wrote:

> Hi Stefan, Li,
>
> > 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().
>
> ksm05.c and ksm06.c does not use create_same_memory(). Or did I overlook
> something?
>

Good catch, I looked into these tests, seems only ksm05 is debatable
for disabling smart_scan, as a simple regression, it suggests disabling
ksm daemon to avoid disturb according to some workload.
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/ksm/ksm05.c#L30

ksm06 is definitely need disable smart_scan, it tests KSM in different
'run' state for merge_accros_nodes.

To be on the safe side, I would suggest applying the patch to all ksm*
tests,
and write a new single for smart_scan if needed.


-- 
Regards,
Li Wang

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

[Petr Vorel]

> On Wed, Nov 29, 2023 at 12:51 AM Petr Vorel <pvorel@suse.cz> wrote:

> > Hi Stefan, Li,

> > > 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().

> > ksm05.c and ksm06.c does not use create_same_memory(). Or did I overlook
> > something?


> Good catch, I looked into these tests, seems only ksm05 is debatable
> for disabling smart_scan, as a simple regression, it suggests disabling
> ksm daemon to avoid disturb according to some workload.
> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/ksm/ksm05.c#L30

> ksm06 is definitely need disable smart_scan, it tests KSM in different
> 'run' state for merge_accros_nodes.

Thanks for having a look.

> To be on the safe side, I would suggest applying the patch to all ksm*
> tests,
> and write a new single for smart_scan if needed.

Agree. I vote for new single for smart_scan related test.

Kind regards,
Petr

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

[Stefan Roesch]

Petr Vorel <pvorel@suse.cz> writes:

>> On Wed, Nov 29, 2023 at 12:51 AM Petr Vorel <pvorel@suse.cz> wrote:
>
>> > Hi Stefan, Li,
>
>> > > 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().
>
>> > ksm05.c and ksm06.c does not use create_same_memory(). Or did I overlook
>> > something?
>
>
>> Good catch, I looked into these tests, seems only ksm05 is debatable
>> for disabling smart_scan, as a simple regression, it suggests disabling
>> ksm daemon to avoid disturb according to some workload.
>> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/ksm/ksm05.c#L30
>
>> ksm06 is definitely need disable smart_scan, it tests KSM in different
>> 'run' state for merge_accros_nodes.
>
> Thanks for having a look.
>
>> To be on the safe side, I would suggest applying the patch to all ksm*
>> tests,
>> and write a new single for smart_scan if needed.
>
> Agree. I vote for new single for smart_scan related test.
>

I'll add a new test.

> Kind regards,
> Petr

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

[Stefan Roesch]

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.

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

[Stefan Roesch]

Petr Vorel <pvorel@suse.cz> writes:

> 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>
>

Thanks, will be fixed with the next version.

>> 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'll add it with the next version

> (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.
>

Other tests will also need it. They also use the create_same_memory()
function.

> 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.
>

This is a different problem. "Smart scan was introduced with 6.7"

>> +
>>  	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