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Message-ID: <20110907065635.GA12619@lst.de>
Date: Wed, 7 Sep 2011 08:56:35 +0200
From: Christoph Hellwig <hch@....de>
To: Jan Kara <jack@...e.cz>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Wu Fengguang <fengguang.wu@...el.com>,
linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Hellwig <hch@....de>,
Dave Chinner <david@...morbit.com>,
Greg Thelen <gthelen@...gle.com>,
Minchan Kim <minchan.kim@...il.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andrea Righi <arighi@...eler.com>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/18] writeback: fix dirtied pages accounting on
redirty
On Wed, Sep 07, 2011 at 02:22:22AM +0200, Jan Kara wrote:
> > So wtf is ext4 doing? Shouldn't a page stay dirty until its written out?
> >
> > That is, should we really frob around this behaviour or fix ext4 because
> > its on crack?
> Fengguang, could you please verify your findings with recent kernel? I
> believe ext4 got fixed in this regard some time ago already (and yes, old
> delalloc writeback code in ext4 was terrible).
The pattern we do in writeback is:
in pageout / write_cache_pages:
lock_page();
clear_page_dirty_for_io();
in ->writepage:
set_page_writeback();
unlock_page();
end_page_writeback();
So whenever ->writepage decides it doesn't want to write things back
we have to redirty pages. We have this happen quite a bit in every
filesystem, but ext4 hits it a lot more than usual because it refuses
to write out delalloc pages from plain ->writepage and only allows
->writepages to do it.
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