From: Mel Gorman <mgorman@suse.de>
To: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
linux-mm@kvack.org, Dave Hansen <dave.hansen@intel.com>,
David Rientjes <rientjes@google.com>
Subject: Re: [RFC] restore user defined min_free_kbytes when disabling thp
Date: Wed, 22 Jan 2014 09:40:53 +0000 [thread overview]
Message-ID: <20140122094053.GT4963@suse.de> (raw)
In-Reply-To: <20140122060506.GA2657@localhost.localdomain>
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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WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@suse.de>
To: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
linux-mm@kvack.org, Dave Hansen <dave.hansen@intel.com>,
David Rientjes <rientjes@google.com>
Subject: Re: [RFC] restore user defined min_free_kbytes when disabling thp
Date: Wed, 22 Jan 2014 09:40:53 +0000 [thread overview]
Message-ID: <20140122094053.GT4963@suse.de> (raw)
In-Reply-To: <20140122060506.GA2657@localhost.localdomain>
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
next prev parent reply other threads:[~2014-01-22 9:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-21 9:38 [RFC] restore user defined min_free_kbytes when disabling thp Han Pingtian
2014-01-21 9:38 ` Han Pingtian
2014-01-21 10:23 ` Mel Gorman
2014-01-21 10:23 ` Mel Gorman
2014-01-22 6:05 ` Han Pingtian
2014-01-22 6:05 ` Han Pingtian
2014-01-22 9:40 ` Mel Gorman [this message]
2014-01-22 9:40 ` Mel Gorman
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