linux-kernel - Re: [PATCH 6/6] vmscan: Kick flusher threads to clean pages when reclaim is encountering dirty pages

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Message-ID: <20100801130300.GA19523@localhost>
Date:	Sun, 1 Aug 2010 21:03:01 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>, pvz@....pp.se,
	bgamari@...il.com, larppaxyz@...il.com, seanj@...e.com,
	kernel-bugs.dev1world@...mgourmet.com, akatopaz@...il.com,
	frankrq2009@....com, thomas.pi@...or.de, spawels13@...il.com,
	vshader@...il.com, rockorequin@...mail.com, ylalym@...il.com,
	theholyettlz@...glemail.com, hassium@...dex.ru
Subject: Re: [PATCH 6/6] vmscan: Kick flusher threads to clean pages when
 reclaim is encountering dirty pages

On Sun, Aug 01, 2010 at 07:56:40PM +0800, Wu Fengguang wrote:
> > Sigh.  We have sooo many problems with writeback and latency.  Read
> > https://bugzilla.kernel.org/show_bug.cgi?id=12309 and weep.  Everyone's
> > running away from the issue and here we are adding code to solve some
> > alleged stack-overflow problem which seems to be largely a non-problem,
> > by making changes which may worsen our real problems.
> 
> I'm sweeping bug 12309. Most people reports some data writes, though
> relative few explicitly stated memory pressure is another necessary
> condition.

#14: Per von Zweigbergk
Ubuntu 2.6.27 slowdown when copying 25MB/s USB stick to 10 MB/s SSD.

KOSAKI and my patches won't fix 2.6.27, since it only do
congestion_wait() and wait_on_page_writeback() for order>3
allocations. There may be more bugs there.

#24: Per von Zweigbergk
The encryption of the SSD very significantly increases the problem.

This is expected. Data encryption roughly doubles page consumption
speed (there may be temp buffers allocated/dropped quickly), hence
vmscan pressure.

#26: Per von Zweigbergk
Disabling swap makes the terminal launch much faster while copying;
However Firefox and vim hang much more aggressively and frequently
during copying.

It's interesting to see processes behave differently. Is this
reproducible at all?

#34: Ben Gamari
There is evidence that x86-64 is a factor here.

Because x86-64 does order-1 page allocation in fork() and consumes
more memory (larger user space code/data)?

#36: Lari Temmes
Go from usable to totally unusable when switching from
a SMP kernel to a UP kernel on a single CPU laptop

He should be testing 2.6.28. I'm not aware of known bugs there.

#47: xyke
Renicing pdflush -10 had some great improvement on basic
responsiveness.

It sure helps :)

Too much (old) messages there. I'm hoping some of the still active
bug reporters to test the following patches (they are for the -mmotm
tree, need to unindent code for Linus's tree) and see if there are
any improvements.

http://lkml.org/lkml/2010/8/1/40
http://lkml.org/lkml/2010/8/1/45

Thanks,
Fengguang
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