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From: Andrew Morton <akpm@linux-foundation.org>
To: Satoru Moriya <satoru.moriya@hds.com>
Cc: David Rientjes <rientjes@google.com>,
	Rik van Riel <riel@redhat.com>,
	Randy Dunlap <rdunlap@xenotime.net>,
	Satoru Moriya <smoriya@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"lwoodman@redhat.com" <lwoodman@redhat.com>,
	Seiji Aguchi <saguchi@redhat.com>,
	"hughd@google.com" <hughd@google.com>,
	"hannes@cmpxchg.org" <hannes@cmpxchg.org>
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable
Date: Tue, 11 Oct 2011 13:54:45 -0700	[thread overview]
Message-ID: <20111011135445.f580749b.akpm@linux-foundation.org> (raw)
In-Reply-To: <65795E11DBF1E645A09CEC7EAEE94B9CB516CBFE@USINDEVS02.corp.hds.com>

On Tue, 11 Oct 2011 16:23:22 -0400
Satoru Moriya <satoru.moriya@hds.com> wrote:

> On 10/11/2011 03:55 PM, Andrew Morton wrote:
> > On Tue, 11 Oct 2011 15:32:11 -0400
> > Satoru Moriya <satoru.moriya@hds.com> wrote:
> > 
> >> On 10/10/2011 06:37 PM, Andrew Morton wrote:
> >>> On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes 
> >>> <rientjes@google.com> wrote:
> >>>
> >>>> On Thu, 1 Sep 2011, Rik van Riel wrote:
> >>
> >> Actually page allocator decreases min watermark to 3/4 * min 
> >> watermark for rt-task. But in our case some applications create a lot 
> >> of processes and if all of them are rt-task, the amount of watermark
> >> bonus(1/4 * min watermark) is not enough.
> >>
> >> If we can tune the amount of bonus, it may be fine. But that is 
> >> almost all same as extra free kbytes.
> > 
> > This situation is detectable at runtime.  If realtime tasks are being 
> > stalled in the page allocator then start to increase the free-page 
> > reserves.  A little control system.
> 
> Detecting at runtime is too late for some latency critical systems.
> At that system, we must avoid a stall before it happens.

It's pretty darn obvious that the kernel can easily see the situation
developing before it happens.  By comparing a few integers.

Look, please don't go bending over backwards like this to defend a bad
patch.  It's a bad patch!  It would be better not to have to merge it. 
Let's do something better.

> Also, if we increase the free-page reserves a.k.a min_free_kbytes,
> the possibility of direct reclaim on other workloads increases.
> I think it's a bad side effect.

extra_free_kbytes has the same side-effect.

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Satoru Moriya <satoru.moriya@hds.com>
Cc: David Rientjes <rientjes@google.com>,
	Rik van Riel <riel@redhat.com>,
	Randy Dunlap <rdunlap@xenotime.net>,
	Satoru Moriya <smoriya@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"lwoodman@redhat.com" <lwoodman@redhat.com>,
	Seiji Aguchi <saguchi@redhat.com>,
	"hughd@google.com" <hughd@google.com>,
	"hannes@cmpxchg.org" <hannes@cmpxchg.org>
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable
Date: Tue, 11 Oct 2011 13:54:45 -0700	[thread overview]
Message-ID: <20111011135445.f580749b.akpm@linux-foundation.org> (raw)
In-Reply-To: <65795E11DBF1E645A09CEC7EAEE94B9CB516CBFE@USINDEVS02.corp.hds.com>

On Tue, 11 Oct 2011 16:23:22 -0400
Satoru Moriya <satoru.moriya@hds.com> wrote:

> On 10/11/2011 03:55 PM, Andrew Morton wrote:
> > On Tue, 11 Oct 2011 15:32:11 -0400
> > Satoru Moriya <satoru.moriya@hds.com> wrote:
> > 
> >> On 10/10/2011 06:37 PM, Andrew Morton wrote:
> >>> On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes 
> >>> <rientjes@google.com> wrote:
> >>>
> >>>> On Thu, 1 Sep 2011, Rik van Riel wrote:
> >>
> >> Actually page allocator decreases min watermark to 3/4 * min 
> >> watermark for rt-task. But in our case some applications create a lot 
> >> of processes and if all of them are rt-task, the amount of watermark
> >> bonus(1/4 * min watermark) is not enough.
> >>
> >> If we can tune the amount of bonus, it may be fine. But that is 
> >> almost all same as extra free kbytes.
> > 
> > This situation is detectable at runtime.  If realtime tasks are being 
> > stalled in the page allocator then start to increase the free-page 
> > reserves.  A little control system.
> 
> Detecting at runtime is too late for some latency critical systems.
> At that system, we must avoid a stall before it happens.

It's pretty darn obvious that the kernel can easily see the situation
developing before it happens.  By comparing a few integers.

Look, please don't go bending over backwards like this to defend a bad
patch.  It's a bad patch!  It would be better not to have to merge it. 
Let's do something better.

> Also, if we increase the free-page reserves a.k.a min_free_kbytes,
> the possibility of direct reclaim on other workloads increases.
> I think it's a bad side effect.

extra_free_kbytes has the same side-effect.

--
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  reply	other threads:[~2011-10-11 20:59 UTC|newest]

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-01 14:52 [PATCH -mm] add extra free kbytes tunable Rik van Riel
2011-09-01 14:52 ` Rik van Riel
2011-09-01 17:06 ` Randy Dunlap
2011-09-01 17:06   ` Randy Dunlap
2011-09-01 19:26   ` [PATCH -v2 " Rik van Riel
2011-09-01 19:26     ` Rik van Riel
2011-09-01 21:58     ` Andrew Morton
2011-09-01 21:58       ` Andrew Morton
2011-09-01 22:08       ` David Rientjes
2011-09-01 22:08         ` David Rientjes
2011-09-01 22:16         ` Andrew Morton
2011-09-01 22:16           ` Andrew Morton
2011-09-02 16:31       ` Satoru Moriya
2011-09-02 16:31         ` Satoru Moriya
2011-10-13  7:33         ` Minchan Kim
2011-10-13  7:33           ` Minchan Kim
2011-10-13  8:09           ` KAMEZAWA Hiroyuki
2011-10-13  8:09             ` KAMEZAWA Hiroyuki
     [not found]       ` <E1FA588BC672D846BDBB452FCA1E308C2389B4@USINDEVS02.corp.hds.com>
2011-09-15  3:33         ` Satoru Moriya
2011-09-15  3:33           ` Satoru Moriya
2011-09-01 22:09     ` Andrew Morton
2011-09-01 22:09       ` Andrew Morton
2011-09-02 16:26       ` [PATCH -mm] fixes & cleanups for "add extra free kbytes tunable" Rik van Riel
2011-09-02 16:26         ` Rik van Riel
2011-09-30 21:43     ` [PATCH -v2 -mm] add extra free kbytes tunable Johannes Weiner
2011-09-30 21:43       ` Johannes Weiner
2011-10-08  3:08     ` David Rientjes
2011-10-08  3:08       ` David Rientjes
2011-10-10 22:37       ` Andrew Morton
2011-10-10 22:37         ` Andrew Morton
2011-10-11 19:32         ` Satoru Moriya
2011-10-11 19:32           ` Satoru Moriya
2011-10-11 19:54           ` Andrew Morton
2011-10-11 19:54             ` Andrew Morton
2011-10-11 20:23             ` Satoru Moriya
2011-10-11 20:23               ` Satoru Moriya
2011-10-11 20:54               ` Andrew Morton [this message]
2011-10-11 20:54                 ` Andrew Morton
2011-10-12 13:09                 ` Rik van Riel
2011-10-12 13:09                   ` Rik van Riel
2011-10-12 19:20                   ` Andrew Morton
2011-10-12 19:20                     ` Andrew Morton
2011-10-12 19:58                     ` Rik van Riel
2011-10-12 19:58                       ` Rik van Riel
2011-10-12 20:26                       ` David Rientjes
2011-10-12 20:26                         ` David Rientjes
2011-10-21 23:48                       ` Satoru Moriya
2011-10-21 23:48                         ` Satoru Moriya
2011-10-23 21:22                         ` David Rientjes
2011-10-23 21:22                           ` David Rientjes
2011-10-25  2:04                           ` Satoru Moriya
2011-10-25  2:04                             ` Satoru Moriya
2011-10-25 21:50                             ` David Rientjes
2011-10-25 21:50                               ` David Rientjes
2011-10-26 18:59                               ` Satoru Moriya
2011-10-26 18:59                                 ` Satoru Moriya
2011-10-12 21:08                 ` Satoru Moriya
2011-10-12 21:08                   ` Satoru Moriya
2011-10-12 22:41                   ` David Rientjes
2011-10-12 22:41                     ` David Rientjes
2011-10-12 23:52                     ` Satoru Moriya
2011-10-12 23:52                       ` Satoru Moriya
2011-10-13  0:01                       ` David Rientjes
2011-10-13  0:01                         ` David Rientjes
2011-10-13  5:35                         ` KAMEZAWA Hiroyuki
2011-10-13  5:35                           ` KAMEZAWA Hiroyuki
2011-10-13 20:55                           ` David Rientjes
2011-10-13 20:55                             ` David Rientjes
2011-10-14 22:16                             ` Satoru Moriya
2011-10-14 22:16                               ` Satoru Moriya
2011-10-14 22:46                               ` David Rientjes
2011-10-14 22:46                                 ` David Rientjes
2011-10-14  5:32                           ` Satoru Moriya
2011-10-14  5:32                             ` Satoru Moriya
2011-10-14  5:06                         ` Satoru Moriya
2011-10-14  5:06                           ` Satoru Moriya
2011-10-11 23:22           ` David Rientjes
2011-10-11 23:22             ` David Rientjes
2011-10-13 16:54             ` Satoru Moriya
2011-10-13 16:54               ` Satoru Moriya
2011-10-13 20:48               ` David Rientjes
2011-10-13 20:48                 ` David Rientjes
2011-10-13 21:11                 ` Rik van Riel
2011-10-13 21:11                   ` Rik van Riel
2011-10-13 22:02                   ` David Rientjes
2011-10-13 22:02                     ` David Rientjes
2011-10-11 19:20       ` Satoru Moriya
2011-10-11 19:20         ` Satoru Moriya
2011-10-11 21:04         ` David Rientjes
2011-10-11 21:04           ` David Rientjes
2011-10-12 13:13           ` Rik van Riel
2011-10-12 13:13             ` Rik van Riel
2011-10-12 20:21             ` David Rientjes
2011-10-12 20:21               ` David Rientjes
2011-10-13  4:13               ` Rik van Riel
2011-10-13  4:13                 ` Rik van Riel
2011-10-13  5:22                 ` David Rientjes
2011-10-13  5:22                   ` David Rientjes
2011-10-22  0:11                   ` Satoru Moriya
2011-10-22  0:11                     ` Satoru Moriya
2011-09-09 23:01 Satoru Moriya
2011-09-09 23:01 ` Satoru Moriya

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