Re: [PATCH]vmscan: fix a livelock in kswapd

From: Mel Gorman
Date: Tue Jul 19 2011 - 04:39:44 EST

On Tue, Jul 19, 2011 at 03:09:27PM +0800, Shaohua Li wrote:
> I'm running a workload which triggers a lot of swap in a machine with 4 nodes.
> After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or
> kswapd2 are keeping running and I can't access filesystem, but most memory is
> free. This looks like a regression since commit 08951e545918c159.
> Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for
> classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if
> all zones have watermark ok, end_zone will keep 0.
> Later sleeping_prematurely() always returns true. Because this is an order 3
> wakeup, and if classzone_idx is 0, both balanced_pages and present_pages
> in pgdat_balanced() are 0.
> We add a special case here. If a zone has no page, we think it's balanced. This
> fixes the livelock.
> Signed-off-by: Shaohua Li <>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

It's also needed for 3.0 and 2.6.39-stable I believe.

Mel Gorman
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