linux-kernel - Re: [PATCH] vmscan: skip freeing memory from zones with lots free

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Date:	Sat, 29 Nov 2008 13:59:21 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH] vmscan: skip freeing memory from zones with lots free

Andrew Morton wrote:
> On Sat, 29 Nov 2008 13:41:34 -0500 Rik van Riel <riel@...hat.com> wrote:
> 
>> Andrew Morton wrote:
>>> On Sat, 29 Nov 2008 12:58:32 -0500 Rik van Riel <riel@...hat.com> wrote:
>>>
>>>>> Will this new patch reintroduce the problem which
>>>>> 26e4931632352e3c95a61edac22d12ebb72038fe fixed?
>> No, that problem is already taken care of by the fact that
>> active pages always get deactivated in the current VM,
>> regardless of whether or not they were referenced.
> 
> err, sorry, that was the wrong commit. 
> 26e4931632352e3c95a61edac22d12ebb72038fe _introduced_ the problem, as
> predicted in the changelog.
> 
> 265b2b8cac1774f5f30c88e0ab8d0bcf794ef7b3 later fixed it up.

The patch I sent in this thread does not do any baling out,
it only skips zones where the number of free pages is more
than 4 times zone->pages_high.

Equal pressure is still applied to the other zones.

This should not be a problem since we do not enter direct
reclaim unless the free pages in every zone in our zonelist
are below zone->pages_low.

Zone skipping is only done by tasks that have been in the
direct reclaim code for a long time.

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