* [RFC] restore user defined min_free_kbytes when disabling thp
@ 2014-01-21 9:38 Han Pingtian
2014-01-21 10:23 ` Mel Gorman
0 siblings, 1 reply; 4+ messages in thread
From: Han Pingtian @ 2014-01-21 9:38 UTC (permalink / raw)
To: linux-kernel
Cc: Andrew Morton, Michal Hocko, Mel Gorman, linux-mm, Dave Hansen,
David Rientjes
The testcase 'thp04' of LTP will enable THP, do some testing, then
disable it if it wasn't enabled. But this will leave a different value
of min_free_kbytes if it has been set by admin. So I think it's better
to restore the user defined value after disabling THP.
---
thp increases the value of min_free_kbytes in initialization. This will
change the user defined value of min_free_kbytes. So try to restore the
value when disabling thp.
Signed-off-by: Han Pingtian <hanpt@linux.vnet.ibm.com>
---
mm/huge_memory.c | 9 +++++++++
1 files changed, 9 insertions(+), 0 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 94a824f..276180b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -164,6 +164,15 @@ static int start_khugepaged(void)
} else if (khugepaged_thread) {
kthread_stop(khugepaged_thread);
khugepaged_thread = NULL;
+
+ if (user_min_free_kbytes >= 0) {
+ pr_info("restore min_free_kbytes from %d to user "
+ "defined %d when stopping khugepaged\n",
+ min_free_kbytes, user_min_free_kbytes);
+
+ min_free_kbytes = user_min_free_kbytes;
+ setup_per_zone_wmarks();
+ }
}
return err;
--
1.7.7.6
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [RFC] restore user defined min_free_kbytes when disabling thp
2014-01-21 9:38 [RFC] restore user defined min_free_kbytes when disabling thp Han Pingtian
@ 2014-01-21 10:23 ` Mel Gorman
2014-01-22 6:05 ` Han Pingtian
0 siblings, 1 reply; 4+ messages in thread
From: Mel Gorman @ 2014-01-21 10:23 UTC (permalink / raw)
To: linux-kernel, Andrew Morton, Michal Hocko, linux-mm, Dave Hansen,
David Rientjes
On Tue, Jan 21, 2014 at 05:38:59PM +0800, Han Pingtian wrote:
> The testcase 'thp04' of LTP will enable THP, do some testing, then
> disable it if it wasn't enabled. But this will leave a different value
> of min_free_kbytes if it has been set by admin. So I think it's better
> to restore the user defined value after disabling THP.
>
Then have LTP record what min_free_kbytes was at the same time THP was
enabled by the test and restore both settings. It leaves a window where
an admin can set an alternative value during the test but that would also
invalidate the test in same cases and gets filed under "don't do that".
--
Mel Gorman
SUSE Labs
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC] restore user defined min_free_kbytes when disabling thp
2014-01-21 10:23 ` Mel Gorman
@ 2014-01-22 6:05 ` Han Pingtian
2014-01-22 9:40 ` Mel Gorman
0 siblings, 1 reply; 4+ messages in thread
From: Han Pingtian @ 2014-01-22 6:05 UTC (permalink / raw)
To: Mel Gorman
Cc: linux-kernel, Andrew Morton, Michal Hocko, linux-mm, Dave Hansen,
David Rientjes
On Tue, Jan 21, 2014 at 10:23:51AM +0000, Mel Gorman wrote:
> On Tue, Jan 21, 2014 at 05:38:59PM +0800, Han Pingtian wrote:
> > The testcase 'thp04' of LTP will enable THP, do some testing, then
> > disable it if it wasn't enabled. But this will leave a different value
> > of min_free_kbytes if it has been set by admin. So I think it's better
> > to restore the user defined value after disabling THP.
> >
>
> Then have LTP record what min_free_kbytes was at the same time THP was
> enabled by the test and restore both settings. It leaves a window where
> an admin can set an alternative value during the test but that would also
> invalidate the test in same cases and gets filed under "don't do that".
>
Because the value is changed in kernel, so it would be better to
restore it in kernel, right? :) I have a v2 patch which will restore
the value only if it isn't set again by user after THP's initialization.
This v2 patch is dependent on the patch 'mm: show message when updating
min_free_kbytes in thp' which has been added to -mm tree, can be found
here:
http://ozlabs.org/~akpm/mmotm/broken-out/mm-show-message-when-updating-min_free_kbytes-in-thp.patch
please have a look. Thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC] restore user defined min_free_kbytes when disabling thp
2014-01-22 6:05 ` Han Pingtian
@ 2014-01-22 9:40 ` Mel Gorman
0 siblings, 0 replies; 4+ messages in thread
From: Mel Gorman @ 2014-01-22 9:40 UTC (permalink / raw)
To: linux-kernel, Andrew Morton, Michal Hocko, linux-mm, Dave Hansen,
David Rientjes
On Wed, Jan 22, 2014 at 02:05:06PM +0800, Han Pingtian wrote:
> On Tue, Jan 21, 2014 at 10:23:51AM +0000, Mel Gorman wrote:
> > On Tue, Jan 21, 2014 at 05:38:59PM +0800, Han Pingtian wrote:
> > > The testcase 'thp04' of LTP will enable THP, do some testing, then
> > > disable it if it wasn't enabled. But this will leave a different value
> > > of min_free_kbytes if it has been set by admin. So I think it's better
> > > to restore the user defined value after disabling THP.
> > >
> >
> > Then have LTP record what min_free_kbytes was at the same time THP was
> > enabled by the test and restore both settings. It leaves a window where
> > an admin can set an alternative value during the test but that would also
> > invalidate the test in same cases and gets filed under "don't do that".
> >
>
> Because the value is changed in kernel, so it would be better to
> restore it in kernel, right? :) I have a v2 patch which will restore
> the value only if it isn't set again by user after THP's initialization.
> This v2 patch is dependent on the patch 'mm: show message when updating
> min_free_kbytes in thp' which has been added to -mm tree, can be found
> here:
>
It still feels like the type of scenario that only shows up during tests
that modify kernel parameters as part of the test. I do not consider it
normal operation for THP to be enabled and disabled multiple types during
the lifetime of the system. If the system started with THP disabled, ran
for a long period of time then the benefit of having min_free_kbytes at
a higher value is already lost due to the system being potentially in a
fragmented state already.
I'm ok with the warning being displayed if min_free_kbytes is updated
but I'm not convinced that further trickery is necessary.
--
Mel Gorman
SUSE Labs
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2014-01-21 9:38 [RFC] restore user defined min_free_kbytes when disabling thp Han Pingtian
2014-01-21 10:23 ` Mel Gorman
2014-01-22 6:05 ` Han Pingtian
2014-01-22 9:40 ` Mel Gorman
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