linux-kernel - Re: Bug in kernel 2.6.31, Slow wb

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Message-ID: <33307c790907301255j136e003dtac0e4ba2032e890e@mail.gmail.com>
Date:	Thu, 30 Jul 2009 12:55:44 -0700
From:	Martin Bligh <mbligh@...gle.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Michael Rubin <mrubin@...gle.com>,
	"sandeen@...hat.com" <sandeen@...hat.com>,
	Michael Davidson <md@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout

> Note that this is a simple fix that may have suboptimal write performance.
> Here is an old reasoning:
>
>        http://lkml.org/lkml/2009/3/28/235

The other thing I've been experimenting with is to disable the per-page
check in write_cache_pages, ie:

                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
                                wb_stats_inc(WB_STATS_WCP_SECTION_CONG);
                                wbc->encountered_congestion = 1;
                                /* done = 1; */

This treats the congestion limits as soft, but encourages us to write
back in larger, more efficient chunks. If that's not going to scare
people unduly, I can submit that as well.
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