From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0
Date: Thu, 12 May 2011 19:51:04 +0200
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Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
        Christoph Lameter <cl@linux.com>, Dave Jones <davej@redhat.com>,
        Mel Gorman <mgorman@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Colin King <colin.king@canonical.com>,
        Raghavendra D Prabhu <raghu.prabhu13@gmail.com>,
        Jan Kara <jack@suse.cz>, Chris Mason <chris.mason@oracle.com>,
        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: Pekka Enberg <penberg@kernel.org>
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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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