linux-kernel - Re: regression in page writeback

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Date:	Tue, 22 Sep 2009 17:54:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"richard@....demon.co.uk" <richard@....demon.co.uk>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>
Subject: Re: regression in page writeback

On Wed, 23 Sep 2009 08:22:20 +0800 Wu Fengguang <fengguang.wu@...el.com> wrote:

> Jens' per-bdi writeback has another improvement. In 2.6.31, when
> superblocks A and B both have 100000 dirty pages, it will first
> exhaust A's 100000 dirty pages before going on to sync B's.

That would only be true if someone broke 2.6.31.  Did they?

SYSCALL_DEFINE0(sync)
{
	wakeup_pdflush(0);
	sync_filesystems(0);
	sync_filesystems(1);
	if (unlikely(laptop_mode))
		laptop_sync_completion();
	return 0;
}

the sync_filesystems(0) is supposed to non-blockingly start IO against
all devices.  It used to do that correctly.  But people mucked with it
so perhaps it no longer does.

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