linux-kernel - Re: Re: -mm merge plans -- lumpy reclaim

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Message-ID: <4694A427.7070708@shadowen.org>
Date:	Wed, 11 Jul 2007 10:34:31 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	Andy Whitcroft <apw@...dowen.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Re: -mm merge plans -- lumpy reclaim

[Seems a PEBKAC occured on the subject line, resending lest it become a
victim of "oh thats spam".]

Andy Whitcroft wrote:
> Andrew Morton wrote:
> 
> [...]
>> lumpy-reclaim-v4.patch
>> have-kswapd-keep-a-minimum-order-free-other-than-order-0.patch
>> only-check-absolute-watermarks-for-alloc_high-and-alloc_harder-allocations.patch
>>
>>  Lumpy reclaim.  In a similar situation to Mel's patches.  Stuck due to
>>  general lack or interest and effort.
> 
> The lumpy reclaim patches originally came out of work to support Mel's
> anti-fragmentation work.  As such I think they have become somewhat
> attached to those patches.  Whilst lumpy is most effective where
> placement controls are in place as offered by Mel's work, we see benefit
> from reduction in the "blunderbuss" effect when we reclaim at higher
> orders.  While placement control is pretty much required for the very
> highest orders such as huge page size, lower order allocations are
> benefited in terms of lower collateral damage.
> 
> There are now a few areas other than huge page allocations which can
> benefit.  Stacks are still order 1.  Jumbo frames want higher order
> contiguous pages for there incoming hardware buffers.  SLUB is showing
> performance benefits from moving to a higher allocation order.  All of
> these should benefit from more aggressive targeted reclaim, indeed I
> have been surprised just how often my test workloads trigger lumpy at
> order 1 to get new stacks.
> 
> Truly representative work loads are hard to generate for some of these.
>  Though we have heard some encouraging noises from those who can
> reproduce these problems.
> 
> [...]
> 
> -apw


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