linux-ext4 - Re: [PATCH 3/3] mm: slub: Default slub_max

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Date:	Thu, 12 May 2011 10:37:09 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Mel Gorman <mgorman@...e.de>,
	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 3/3] mm: slub: Default slub_max_order to 0

On Thu, 12 May 2011 18:10:38 +0200 Eric Dumazet <eric.dumazet@...il.com> wrote:

> More fuel to this discussion with commit 6d4831c2
> 
> Something is wrong with high order allocations, on some machines.
> 
> Maybe we can find real cause instead of limiting us to use order-0 pages
> in the end... ;)
> 
> commit 6d4831c283530a5f2c6bd8172c13efa236eb149d
> Author: Andrew Morton <akpm@...ux-foundation.org>
> Date:   Wed Apr 27 15:26:41 2011 -0700
> 
>     vfs: avoid large kmalloc()s for the fdtable

Well, it's always been the case that satisfying higher-order
allocations take a disproportionate amount of work in page reclaim. 
And often causes excessive reclaim.

That's why we've traditionally worked to avoid higher-order
allocations, and this has always been a problem with slub.

But the higher-order allocations shouldn't cause the VM to melt down. 
We changed something, and now it melts down.  Changing slub to avoid
that meltdown doesn't fix the thing we broke.

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