linux-kernel - Re: [PATCH 0/8] Avoiding fragmentation with subzone groupings v25

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Message-ID: <Pine.LNX.4.64.0609081020490.7094@skynet.skynet.ie>
Date:	Fri, 8 Sep 2006 10:24:59 +0100 (IST)
From:	Mel Gorman <mel@....ul.ie>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...l.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] Avoiding fragmentation with subzone groupings v25

On Fri, 8 Sep 2006, Peter Zijlstra wrote:

> On Thu, 2006-09-07 at 17:58 -0700, Andrew Morton wrote:
>> On Thu,  7 Sep 2006 20:03:42 +0100 (IST)
>> Mel Gorman <mel@....ul.ie> wrote:
>>
>>> When a page is allocated, the page-flags
>>> are updated with a value indicating it's type of reclaimability so that it
>>> is placed on the correct list on free.
>>
>> We're getting awful tight on page-flags.
>>
>> Would it be possible to avoid adding the flag?  Say, have a per-zone bitmap
>> of size (zone->present_pages/(1<<MAX_ORDER)) bits, then do a lookup in
>> there to work out whether a particular page is within a MAX_ORDER clump of
>> easy-reclaimable pages?
>
> That would not actually work, the fallback allocation path can move
> blocks smaller than MAX_ORDER to another recaim type.
>

Believe it or not, it may be desirably to have a whole block represented 
by one or two bits. If a fallback allocation occurs and I move blocks 
between lists, I want pages that free later to be freed to the new list as 
well. Currently that doesn't happen because the flags are set per-page but 
it used to happen in an early version of anti-frag.

> But yeah, page flags are getting right, perhaps Rafael can use his
> recently introduced bitmaps to rid us of the swsusp flags?
>
>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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