From: Jan Kara <jack@suse.cz>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
Wu Fengguang <fengguang.wu@intel.com>,
linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Dave Chinner <david@fromorbit.com>,
Greg Thelen <gthelen@google.com>,
Minchan Kim <minchan.kim@gmail.com>,
Vivek Goyal <vgoyal@redhat.com>,
Andrea Righi <arighi@develer.com>, linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 17/18] writeback: fix dirtied pages accounting on redirty
Date: Wed, 7 Sep 2011 18:42:16 +0200 [thread overview]
Message-ID: <20110907164216.GA7725@quack.suse.cz> (raw)
In-Reply-To: <1315383587.11101.18.camel@twins>
On Wed 07-09-11 10:19:47, Peter Zijlstra wrote:
> On Wed, 2011-09-07 at 08:56 +0200, Christoph Hellwig wrote:
> > 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.
>
> Ah, right, so it is a fairly common thing and not something easily fixed
> in filesystems.
Well, it depends on what you call common - usually, ->writepage is called
from kswapd which shouldn't be common compared to writeback from a flusher
thread. But now I've realized that JBD2 also calls ->writepage to fulfill
data=ordered mode guarantees and that's what causes most of redirtying of
pages on ext4. That's going away eventually but it will take some time. So
for now writeback has to handle redirtying...
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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next prev parent reply other threads:[~2011-09-07 16:42 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-04 1:53 [PATCH 00/18] IO-less dirty throttling v11 Wu Fengguang
2011-09-04 1:53 ` [PATCH 01/18] writeback: account per-bdi accumulated dirtied pages Wu Fengguang
2011-09-04 1:53 ` [PATCH 02/18] writeback: dirty position control Wu Fengguang
2011-09-05 15:02 ` Peter Zijlstra
2011-09-06 2:10 ` Wu Fengguang
2011-09-05 15:05 ` Peter Zijlstra
2011-09-06 2:43 ` Wu Fengguang
2011-09-06 18:20 ` Vivek Goyal
2011-09-08 2:53 ` Wu Fengguang
2011-11-12 5:44 ` Nai Xia
2011-09-04 1:53 ` [PATCH 03/18] writeback: dirty rate control Wu Fengguang
2011-09-29 11:57 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 04/18] writeback: stabilize bdi->dirty_ratelimit Wu Fengguang
2011-09-04 1:53 ` [PATCH 05/18] writeback: per task dirty rate limit Wu Fengguang
2011-09-06 15:47 ` Peter Zijlstra
2011-09-06 23:27 ` Jan Kara
2011-09-06 23:34 ` Jan Kara
2011-09-07 7:27 ` Peter Zijlstra
2011-09-07 1:04 ` Wu Fengguang
2011-09-07 7:31 ` Peter Zijlstra
2011-09-07 11:00 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 06/18] writeback: IO-less balance_dirty_pages() Wu Fengguang
2011-09-06 12:13 ` Peter Zijlstra
2011-09-07 2:46 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 07/18] writeback: dirty ratelimit - think time compensation Wu Fengguang
2011-09-04 1:53 ` [PATCH 08/18] writeback: trace dirty_ratelimit Wu Fengguang
2011-09-04 1:53 ` [PATCH 09/18] writeback: trace balance_dirty_pages Wu Fengguang
2011-09-04 1:53 ` [PATCH 10/18] writeback: dirty position control - bdi reserve area Wu Fengguang
2011-09-06 14:09 ` Peter Zijlstra
2011-09-07 12:31 ` Wu Fengguang
2011-09-12 10:19 ` Peter Zijlstra
2011-09-18 14:17 ` Wu Fengguang
2011-09-18 14:37 ` Wu Fengguang
2011-09-18 14:47 ` Wu Fengguang
2011-09-28 14:02 ` Wu Fengguang
2011-09-28 14:50 ` Peter Zijlstra
2011-09-29 3:32 ` Wu Fengguang
2011-09-29 8:49 ` Peter Zijlstra
2011-09-29 11:05 ` Wu Fengguang
2011-09-29 12:15 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 11/18] block: add bdi flag to indicate risk of io queue underrun Wu Fengguang
2011-09-06 14:22 ` Peter Zijlstra
2011-09-07 2:37 ` Wu Fengguang
2011-09-07 7:31 ` Peter Zijlstra
2011-09-04 1:53 ` [PATCH 12/18] writeback: balanced_rate cannot exceed write bandwidth Wu Fengguang
2011-09-04 1:53 ` [PATCH 13/18] writeback: limit max dirty pause time Wu Fengguang
2011-09-06 14:52 ` Peter Zijlstra
2011-09-07 2:35 ` Wu Fengguang
2011-09-12 10:22 ` Peter Zijlstra
2011-09-18 14:23 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 14/18] writeback: control " Wu Fengguang
2011-09-06 15:51 ` Peter Zijlstra
2011-09-07 2:02 ` Wu Fengguang
2011-09-12 10:28 ` Peter Zijlstra
2011-09-04 1:53 ` [PATCH 15/18] writeback: charge leaked page dirties to active tasks Wu Fengguang
2011-09-06 16:16 ` Peter Zijlstra
2011-09-07 9:06 ` Wu Fengguang
2011-09-07 0:17 ` Jan Kara
2011-09-07 9:37 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 16/18] writeback: fix dirtied pages accounting on sub-page writes Wu Fengguang
2011-09-04 1:53 ` [PATCH 17/18] writeback: fix dirtied pages accounting on redirty Wu Fengguang
2011-09-06 16:18 ` Peter Zijlstra
2011-09-07 0:22 ` Jan Kara
2011-09-07 1:18 ` Wu Fengguang
2011-09-07 6:56 ` Christoph Hellwig
2011-09-07 8:19 ` Peter Zijlstra
2011-09-07 16:42 ` Jan Kara [this message]
2011-09-07 16:46 ` Christoph Hellwig
2011-09-08 8:51 ` Steven Whitehouse
2011-09-04 1:53 ` [PATCH 18/18] btrfs: fix dirtied pages accounting on sub-page writes Wu Fengguang
2011-09-07 13:32 ` [PATCH 00/18] IO-less dirty throttling v11 Wu Fengguang
2011-09-07 19:14 ` Trond Myklebust
2011-09-28 14:58 ` Christoph Hellwig
2011-09-29 4:11 ` Wu Fengguang
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