linux-kernel - Re: [15/17] SLUB: Support virtual fallback via SLAB

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Message-Id: <200709301416.10033.nickpiggin@yahoo.com.au>
Date:	Sun, 30 Sep 2007 14:16:09 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <clameter@....com>,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK

On Monday 01 October 2007 06:12, Andrew Morton wrote:
> On Sun, 30 Sep 2007 05:09:28 +1000 Nick Piggin <nickpiggin@...oo.com.au> 
wrote:
> > On Sunday 30 September 2007 05:20, Andrew Morton wrote:

> > > We can't "run out of unfragmented memory" for an order-2 GFP_KERNEL
> > > allocation in this workload.  We go and synchronously free stuff up to
> > > make it work.
> > >
> > > How did this get broken?
> >
> > Either no more order-2 pages could be freed, or the ones that were being
> > freed were being used by something else (eg. other order-2 slab
> > allocations).
>
> No.  The current design of reclaim (for better or for worse) is that for
> order 0,1,2 and 3 allocations we just keep on trying until it works.  That
> got broken and I think it got broken at a design level when that
> did_some_progress logic went in.  Perhaps something else we did later
> worsened things.

It will keep trying until it works. It won't have stopped trying (unless
I'm very mistaken?), it's just oom killing things merrily along the way.
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