Re: [PATCH 2/4] mm: slub: Do not wake kswapd for SLUBs speculativehigh-order allocations

From: Christoph Lameter
Date: Wed May 18 2011 - 13:21:22 EST

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@xxxxxxx>
> > Acked-by: David Rientjes<rientjes@xxxxxxxxxx>
> 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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