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

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Date:	Sat, 29 Nov 2008 12:58:32 -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 11:47:25 -0500 Rik van Riel <riel@...hat.com> wrote:
> 
>> Andrew Morton wrote:
>>
>>>> Index: linux-2.6.28-rc5/mm/vmscan.c
>>>> ===================================================================
>>>> --- linux-2.6.28-rc5.orig/mm/vmscan.c	2008-11-28 05:53:56.000000000 -0500
>>>> +++ linux-2.6.28-rc5/mm/vmscan.c	2008-11-28 06:05:29.000000000 -0500
>>>> @@ -1510,6 +1510,9 @@ static unsigned long shrink_zones(int pr
>>>>  			if (zone_is_all_unreclaimable(zone) &&
>>>>  						priority != DEF_PRIORITY)
>>>>  				continue;	/* Let kswapd poll it */
>>>> +			if (zone_watermark_ok(zone, sc->order,
>>>> +					4*zone->pages_high, high_zoneidx, 0))
>>>> +				continue;	/* Lots free already */
>>>>  			sc->all_unreclaimable = 0;
>>>>  		} else {
>>>>  			/*
>>> We already tried this, or something very similar in effect, I think...
>> Yes, we have a check just like this in balance_pgdat().
>>
>> It's been there forever with no ill effect.
> 
> This patch affects direct reclaim as well as kswapd.

No, kswapd calls shrink_zone directly from balance_pgdat,
it does not go through shrink_zones.

>>> commit 26e4931632352e3c95a61edac22d12ebb72038fe
>>> Author: akpm <akpm>
>>> Date:   Sun Sep 8 19:21:55 2002 +0000
>>>
>>>     [PATCH] refill the inactive list more quickly
>>>     
>>>     Fix a problem noticed by Ed Tomlinson: under shifting workloads the
>>>     shrink_zone() logic will refill the inactive load too slowly.
>>>     
>>>     Bale out of the zone scan when we've reclaimed enough pages.  Fixes a
>>>     rarely-occurring problem wherein refill_inactive_zone() ends up
>>>     shuffling 100,000 pages and generally goes silly.
>> This is not a bale out, this is a "skip zones that have way
>> too many free pages already".
> 
> It is similar in effect.
> 
> Will this new patch reintroduce the problem which
> 26e4931632352e3c95a61edac22d12ebb72038fe fixed?

Googling on 26e4931632352e3c95a61edac22d12ebb72038fe only finds
your emails with that commit id in it - which git tree do I
need to search to get that changeset?

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