APPLIED: Natty SRU: vmscan: fix a livelock in kswapd
On 07/20/2011 02:47 PM, Tim Gardner wrote:
From 64ba82a4b63a45fd0c102dd97ea81c59fc522b76 Mon Sep 17 00:00:00 2001
From: Shaohua Li<email@example.com>
Date: Tue, 19 Jul 2011 08:49:26 -0700
Subject: [PATCH] vmscan: fix a livelock in kswapd
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 ("mm: vmscan:
correct check for kswapd sleeping in sleeping_prematurely").
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.