linux-kernel - Re: [PATCH] mm: use global_dirty_limit in throttle_vm

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Date:	Mon, 19 Mar 2012 08:37:13 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Greg Thelen <gthelen@...gle.com>,
	Ying Han <yinghan@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: use global_dirty_limit in throttle_vm_writeout()

On Fri, Mar 02, 2012 at 02:14:51PM +0800, Fengguang Wu wrote:
> When starting a memory hog task, a desktop box w/o swap is found to go
> unresponsive for a long time. It's solely caused by lots of congestion
> waits in throttle_vm_writeout():
> 
>  gnome-system-mo-4201 553.073384: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
>  gnome-system-mo-4201 553.073386: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
>            gtali-4237 553.080377: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
>            gtali-4237 553.080378: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
>             Xorg-3483 553.103375: congestion_wait: throttle_vm_writeout+0x70/0x7f shrink_mem_cgroup_zone+0x48f/0x4a1
>             Xorg-3483 553.103377: writeback_congestion_wait: usec_timeout=100000 usec_delayed=100000
> 
> The root cause is, the dirty threshold is knocked down a lot by the
> memory hog task. Fixed by using global_dirty_limit which decreases
> gradually on such events and can guarantee we stay above (the also
> decreasing) nr_dirty in the progress of following down to the new
> dirty threshold.
> 
> Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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