linux-kernel - Re: [PATCH 2.6.27.y 1/3] ext4: Use our own write_cache

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Message-ID: <4C0070D8.8060500@jaysonking.com>
Date:	Fri, 28 May 2010 20:41:44 -0500
From:	"Jayson R. King" <dev@...sonking.com>
To:	tytso@....edu
CC:	"Jayson R. King" <dev@...sonking.com>,
	Stable team <stable@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Dave Chinner <david@...morbit.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Kay Diederichs <Kay.Diederichs@...-konstanz.de>
Subject: Re: [PATCH 2.6.27.y 1/3] ext4: Use our own write_cache_pages()

On 05/28/2010 07:49 PM, tytso@....edu wrote:
> This doesn't fix a bug; it's to make it easy for Dave Chinner to make
> some changes to fix XFS's performance and to undo some ext4-specific
> changes to write_cache_pages().  I'm not sure there's a good reason to
> backport this to 2.6.27.y....

The difference is that, 2.6.27's write_cache_pages() in page-writeback.c 
still updates wbc->nr_to_write, since the patch which changed that 
behavior was dropped from .27-rc2 due to the XFS regression it causes on 
mainline. ext4 appears to want the behavior of write_cache_pages which 
does not update wbc->nr_to_write. This write_cache_pages_da() does what 
ext4 wants, without introducing the XFS regression. So I believe it is 
needed.

Did I mis-judge?

Rgds,

Jayson
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