Date: Wed, 18 May 2011 12:21:08 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
cc: David Rientjes <rientjes@google.com>, Mel Gorman <mgorman@suse.de>,
        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>,
        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>
Subject: Re: [PATCH 2/4] mm: slub: Do not wake kswapd for SLUBs speculative
 high-order allocations
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On Wed, 18 May 2011, Pekka Enberg wrote:

> On 5/17/11 12:10 AM, David Rientjes wrote:
> > On Fri, 13 May 2011, Mel Gorman wrote:
> >
> > > To avoid locking and per-cpu overhead, SLUB optimisically uses
> > > high-order allocations and falls back to lower allocations if they
> > > fail.  However, by simply trying to allocate, kswapd is woken up to
> > > start reclaiming at that order. On a desktop system, two users report
> > > that the system is getting locked up with kswapd using large amounts
> > > of CPU.  Using SLAB instead of SLUB made this problem go away.
> > >
> > > This patch prevents kswapd being woken up for high-order allocations.
> > > Testing indicated that with this patch applied, the system was much
> > > harder to hang and even when it did, it eventually recovered.
> > >
> > > Signed-off-by: Mel Gorman<mgorman@suse.de>
> > Acked-by: David Rientjes<rientjes@google.com>
>
> Christoph? I think this patch is sane although the original rationale was to
> workaround kswapd problems.

I am mostly fine with it. The concerns that I have is if there is a
large series of high order allocs then at some point you would want
kswapd to be triggered instead of high order allocs constantly failing.

Can we have a "trigger once in a while" functionality?

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