linux-ext4 - [PATCH 0/2] Eliminate hangs when using frequent high-order allocations V3

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Date:	Mon, 16 May 2011 16:06:55 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	stable <stable@...nel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 0/2] Eliminate hangs when using frequent high-order allocations V3

Changelog since V2
  o Drop all SLUB latency-reducing patches.

Changelog since V1
  o kswapd should sleep if need_resched
  o Remove __GFP_REPEAT from GFP flags when speculatively using high
    orders so direct/compaction exits earlier
  o Remove __GFP_NORETRY for correctness
  o Correct logic in sleeping_prematurely
  o Leave SLUB using the default slub_max_order

There are a few reports of people experiencing hangs when copying
large amounts of data with kswapd using a large amount of CPU which
appear to be due to recent reclaim changes. SLUB using high orders
is the trigger but not the root cause as SLUB has been using high
orders for a while. The root cause was bugs introduced into reclaim
which are addressed by the following two patches.

Patch 1 corrects logic introduced by commit [1741c877: mm:
	kswapd: keep kswapd awake for high-order allocations until
	a percentage of the node is balanced] to allow kswapd to
	go to sleep when balanced for high orders.

Patch 2 notes that even when kswapd is failing to keep up with
	allocation requests, it should still go to sleep when its
	quota has expired to prevent it spinning.

This version drops the patches whereby SLUB avoids expensive steps in
the page allocator, reclaim and compaction due to a lack of agreement
on whether it was an appropriate step or not and not being critical
to resolve the hang. Chris Wood reports that these two patches in
isolation are sufficient to prevent the system hanging.

These should be also considered for -stable for 2.6.38.

-- 
1.7.3.4

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