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

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Message-ID: <20110512175104.GM11579@random.random>
Date:	Thu, 12 May 2011 19:51:04 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	Christoph Lameter <cl@...ux.com>,
	Dave Jones <davej@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	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, May 12, 2011 at 08:11:05PM +0300, Pekka Enberg wrote:
> If it's this:
> 
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=blob_plain;f=config-x86_64-generic;hb=HEAD
> 
> I'd love to see what happens if you disable
> 
> CONFIG_TRANSPARENT_HUGEPAGE=y
> 
> because that's going to reduce high order allocations as well, no?

Well THP forces COMPACTION=y so lumpy won't risk to be activated. I
got once a complaint asking not to make THP force COMPACTION=y (there
is no real dependency here, THP will just call alloc_pages with
__GFP_NO_KSWAPD and order 9, or 10 on x86-nopae), but I preferred to
keep it forced exactly to avoid issues like these when THP is on. If
even order 3 is causing troubles (which doesn't immediately make lumpy
activated, it only activates when priority is < DEF_PRIORITY-2, so
after 2 loops failing to reclaim nr_to_reclaim pages), imagine what
was happening at order 9 every time firefox, gcc and mutt allocated
memory ;).
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