Date: Tue, 18 Sep 2007 11:03:37 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: use pagevec to rotate reclaimable page
Message-Id: <20070918110337.7d23b3aa.akpm@linux-foundation.org>
In-Reply-To: <200709181147.45006.nickpiggin@yahoo.com.au>
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On Tue, 18 Sep 2007 11:47:44 +1000 Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> On Wednesday 19 September 2007 03:44, Andrew Morton wrote:
> > On Tue, 18 Sep 2007 11:29:50 +1000 Nick Piggin <nickpiggin@yahoo.com.au> 
> wrote:
> > > It would be interesting to test -mm kernels. They have a patch which
> > > reduces zone lock contention quite a lot.
> >
> > They do?  Which patch?
> 
> Hmm... mm-buffered-write-cleanup.patch.

hmm.

> 
> > > I think your patch is a nice idea, and with less zone lock contention in
> > > other areas, it is possible that it might produce a relatively larger
> > > improvement.
> >
> > I'm a bit wobbly about this patch - it adds additional single-cpu overhead
> > to reduce multiple-cpu overhead and latency.
> 
> Yeah, that's true. Although maybe it gets significantly more after the
> patch in -mm.
> 
> Possibly other page batching sites have similar issues on UP... I wonder
> if a type of pagevec that turns into a noop on UP would be interesting...
> probably totally unmeasurable and not worth the cost of code
> maintenance ;)

Yes, I wonder that.  Some of the additional overhead will come from
the additional get_page/put_page which is needed for pagevec ownership.
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