linux-ext4 - Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations

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Message-ID: <alpine.DEB.2.00.1105171251450.15604@router.home>
Date:	Tue, 17 May 2011 12:52:14 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs
 speculative high-order allocations

On Tue, 17 May 2011, Mel Gorman wrote:

> > That is not what I meant. I would like more higher order allocations to
> > succeed. That does not mean that slubs allocation methods and flags passed
> > have to stay the same. You can change the slub behavior if it helps.
> >
>
> In this particular patch, the success rate for high order allocations
> would likely decrease in low memory conditions albeit the latency when
> calling the page allocator will be lower and the disruption to the
> system will be less (no copying or reclaim of pages). My expectation
> would be that it's cheaper for SLUB to fall back than compact memory
> or reclaim pages even if this means a slab page is smaller until more
> memory is free. However, if the "goodness" criteria is high order
> allocation success rate, the patch shouldn't be merged.

The criteria is certainly overall system performance and not a high order
allocation rate.
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