linux-kernel - Re: [PATCH 0/11] Reduce compaction-related stalls and improve asynchronous migration of dirty pages v6

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Message-Id: <20111216145600.908fc77e.akpm@linux-foundation.org>
Date:	Fri, 16 Dec 2011 14:56:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Dave Jones <davej@...hat.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>, Nai Xia <nai.xia@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/11] Reduce compaction-related stalls and improve
 asynchronous migration of dirty pages v6

On Wed, 14 Dec 2011 15:41:22 +0000
Mel Gorman <mgorman@...e.de> wrote:

> Short summary: There are severe stalls when a USB stick using VFAT
> is used with THP enabled that are reduced by this series. If you are
> experiencing this problem, please test and report back and considering
> I have seen complaints from openSUSE and Fedora users on this as well
> as a few private mails, I'm guessing it's a widespread issue. This
> is a new type of USB-related stall because it is due to synchronous
> compaction writing where as in the past the big problem was dirty
> pages reaching the end of the LRU and being written by reclaim.
> 
> Am cc'ing Andrew this time and this series would replace
> mm-do-not-stall-in-synchronous-compaction-for-thp-allocations.patch.
> I'm also cc'ing Dave Jones as he might have merged that patch to Fedora
> for wider testing and ideally it would be reverted and replaced by
> this series.

So it appears that the problem is painful for distros and users and
that we won't have this fixed until 3.2 at best, and that fix will be a
difficult backport for distributors of earlier kernels.

To serve those people better, I'm wondering if we should merge
mm-do-not-stall-in-synchronous-compaction-for-thp-allocations now, make
it available for -stable backport and then revert it as part of this
series?   ie: give people a stopgap while we fix it properly?

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