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Date: Mon, 05 Mar 2012 15:06:14 -0500
From: Rik van Riel <riel@redhat.com>
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To: Fengguang Wu <fengguang.wu@intel.com>
CC: Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
        Greg Thelen <gthelen@google.com>, Ying Han <yinghan@google.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Mel Gorman <mgorman@suse.de>, Minchan Kim <minchan.kim@gmail.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: use global_dirty_limit in throttle_vm_writeout()
References: <20120302061451.GA6468@localhost>
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On 03/02/2012 01:14 AM, 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@intel.com>

Reviewed-by: Rik van Riel <riel@redhat.com>