linux-kernel - Re: [RFC] [PATCH] Avoid livelock for fsync

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Message-Id: <200910271926.15176.knikanth@suse.de>
Date:	Tue, 27 Oct 2009 19:26:14 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Jan Kara <jack@...e.cz>
Cc:	WU Fengguang <wfg@...l.ustc.edu.cn>, npiggin@...e.de,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	hch@...radead.org, chris.mason@...cle.com
Subject: Re: [RFC] [PATCH] Avoid livelock for fsync

On Monday 26 October 2009 23:43:14 Jan Kara wrote:
>   Hi,
> 
>   on my way back from Kernel Summit, I've coded the attached patch which
> implements livelock avoidance for write_cache_pages. We tag patches that
> should be written in the beginning of write_cache_pages and then write
> only tagged pages (see the patch for details). The patch is based on Nick's
> idea.

As I understand, livelock can be caused only by dirtying new pages.

So theoretically, if a process can dirty pages faster than we can tag pages 
for writeback, even now isn't there a chance for livelock? But if it is really 
a very fast operation and livelock is not possible, why not hold the tree_lock 
during the entire period of tagging the pages for writeback i.e., call 
tag_pages_for_writeback() under mapping->tree_lock? Would it cause 
deadlock/starvation or some other serious problems?

Thanks
Nikanth
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