linux-kernel - Re: [PATCH] Improve buffered streaming write ordering

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Message-ID: <20081007133651.GA19895@infradead.org>
Date:	Tue, 7 Oct 2008 09:36:51 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Theodore Tso <tytso@....edu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Chris Mason <chris.mason@...cle.com>,
	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] Improve buffered streaming write ordering

On Tue, Oct 07, 2008 at 09:29:11AM -0400, Theodore Tso wrote:
> That's true, but there is a lot of code duplication, which means that
> bugs or changes in write_cache_pages() would need to be fixed in
> ext4_write_cache_pages().  So another approach that might be better
> from a long-term code maintenance point of view is to add a flag in
> struct writeback_control that tells write_cache_pages() not to update
> those fields, and avoid duplicating approximately 95 lines of code.
> It means a change in a core mm function, though, so if folks thinks
> its too ugly, we can make our own copy in fs/ext4.
> 
> Opinions?  Andrew, as someone who often weighs in on fs and mm issues,
> what do you think?  My preference would be to make the change to
> mm/page-writeback.c, controlled by a flag which ext4 would set be set
> by fs/ext4 before it calls write_cache_pages().

I agree.  But I'm still not quite sure if that requirement is unique to
ext4 anyway.  Give me some time to dive into the writeback code again,
haven't been there for quite a while.

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