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From: Minchan Kim <minchan@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: Jim Schutt <jaschut@sandia.gov>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>
Subject: Re: excessive CPU utilization by isolate_freepages?
Date: Thu, 28 Jun 2012 09:55:46 +0900	[thread overview]
Message-ID: <4FEBAB92.4090206@kernel.org> (raw)
In-Reply-To: <4FEBA520.4030205@redhat.com>

On 06/28/2012 09:28 AM, Rik van Riel wrote:

> On 06/27/2012 07:59 PM, Minchan Kim wrote:
> 
>> I doubt compaction try to migrate continuously although we have no
>> free memory.
>> Could you apply this patch and retest?
>>
>> https://lkml.org/lkml/2012/6/21/30
> 
> Another possibility is that compaction is succeeding every time,
> but since we always start scanning all the way at the beginning
> and end of each zone, we waste a lot of CPU time rescanning the
> same pages (that we just filled up with moved pages) to see if
> any are free.


It does make sense.

> 
> In short, due to the way compaction behaves right now,
> compaction + isolate_freepages are essentially quadratic.
> 
> What we need to do is remember where we left off after a
> successful compaction, so we can continue the search there
> at the next invocation.
> 


Good idea.
It could enhance parallel compaction, too.
Of course, if we can't meet the goal, we need loop around from start/end of zone.

-- 
Kind regards,
Minchan Kim

WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: Jim Schutt <jaschut@sandia.gov>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>
Subject: Re: excessive CPU utilization by isolate_freepages?
Date: Thu, 28 Jun 2012 09:55:46 +0900	[thread overview]
Message-ID: <4FEBAB92.4090206@kernel.org> (raw)
In-Reply-To: <4FEBA520.4030205@redhat.com>

On 06/28/2012 09:28 AM, Rik van Riel wrote:

> On 06/27/2012 07:59 PM, Minchan Kim wrote:
> 
>> I doubt compaction try to migrate continuously although we have no
>> free memory.
>> Could you apply this patch and retest?
>>
>> https://lkml.org/lkml/2012/6/21/30
> 
> Another possibility is that compaction is succeeding every time,
> but since we always start scanning all the way at the beginning
> and end of each zone, we waste a lot of CPU time rescanning the
> same pages (that we just filled up with moved pages) to see if
> any are free.


It does make sense.

> 
> In short, due to the way compaction behaves right now,
> compaction + isolate_freepages are essentially quadratic.
> 
> What we need to do is remember where we left off after a
> successful compaction, so we can continue the search there
> at the next invocation.
> 


Good idea.
It could enhance parallel compaction, too.
Of course, if we can't meet the goal, we need loop around from start/end of zone.

-- 
Kind regards,
Minchan Kim

--
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  parent reply	other threads:[~2012-06-28  0:55 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-06-27 21:59 excessive CPU utilization by isolate_freepages? Jim Schutt
2012-06-27 21:59 ` Jim Schutt
2012-06-27 22:35 ` Mark Nelson
2012-06-27 22:35   ` Mark Nelson
2012-06-27 23:59 ` Minchan Kim
2012-06-27 23:59   ` Minchan Kim
2012-06-28  0:28   ` Rik van Riel
2012-06-28  0:28     ` Rik van Riel
2012-06-28  0:52     ` David Rientjes
2012-06-28  0:52       ` David Rientjes
2012-06-28  0:58       ` Minchan Kim
2012-06-28  0:58         ` Minchan Kim
2012-06-28  1:06         ` David Rientjes
2012-06-28  1:06           ` David Rientjes
2012-06-28  1:18           ` Minchan Kim
2012-06-28  1:18             ` Minchan Kim
2012-06-28  1:13       ` Rik van Riel
2012-06-28  1:13         ` Rik van Riel
2012-06-28  0:55     ` Minchan Kim [this message]
2012-06-28  0:55       ` Minchan Kim
2012-06-28 11:36 ` Mel Gorman
2012-06-28 11:36   ` Mel Gorman
2012-06-28 15:30   ` Jim Schutt
2012-06-28 15:30     ` Jim Schutt

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