From: Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH 3/4] mm: slub: Do not take expensive steps for SLUBs
 speculative high-order allocations
Date: Tue, 17 May 2011 12:52:14 -0500 (CDT)
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Cc: David Rientjes <rientjes@google.com>,
  Andrew Morton <akpm@linux-foundation.org>,
  James Bottomley <James.Bottomley@hansenpartnership.com>,
  Colin King <colin.king@canonical.com>,
  Raghavendra D Prabhu <raghu.prabhu13@gmail.com>, Jan Kara <jack@suse.cz>,
  Chris Mason <chris.mason@oracle.com>, Pekka Enberg <penberg@kernel.org>,
  Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
  linux-fsdevel <linux-fsdevel@vger.kernel.org>,
  linux-mm <linux-mm@kvack.org>, linux-kernel <linux-kernel@vger.kernel.org>,
  linux-ext4 <linux-ext4@vger.kernel.org>
To: Mel Gorman <mgorman@suse.de>
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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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