From: Dave Chinner <david@fromorbit.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Mel Gorman <mel@linux.vnet.ibm.com>,
Mel Gorman <mel@csn.ul.ie>,
Itaru Kitayama <kitayama@cl.bb4u.ne.jp>,
Trond Myklebust <Trond.Myklebust@netapp.com>,
Minchan Kim <minchan.kim@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH 2/6] writeback: the kupdate expire timestamp should be a moving target
Date: Tue, 19 Apr 2011 17:02:47 +1000 [thread overview]
Message-ID: <20110419070247.GE23985@dastard> (raw)
In-Reply-To: <20110419030532.392203618@intel.com>
On Tue, Apr 19, 2011 at 11:00:05AM +0800, Wu Fengguang wrote:
> Dynamically compute the dirty expire timestamp at queue_io() time.
>
> writeback_control.older_than_this used to be determined at entrance to
> the kupdate writeback work. This _static_ timestamp may go stale if the
> kupdate work runs on and on. The flusher may then stuck with some old
> busy inodes, never considering newly expired inodes thereafter.
>
> This has two possible problems:
>
> - It is unfair for a large dirty inode to delay (for a long time) the
> writeback of small dirty inodes.
>
> - As time goes by, the large and busy dirty inode may contain only
> _freshly_ dirtied pages. Ignoring newly expired dirty inodes risks
> delaying the expired dirty pages to the end of LRU lists, triggering
> the evil pageout(). Nevertheless this patch merely addresses part
> of the problem.
When wb_writeback() is called with for_kupdate set, it initialises
wbc->older_than_this appropriately outside the writeback loop.
queue_io() is called once per writeback_inodes_wb() call, which is
once per loop in wb_writeback. All your change does is re-initialise
older_than_this once per loop in wb_writeback, jus tin a different
and very non-obvious place.
So why didn't you just re-initialise it inside the loop in
wb_writeback() and leave all the other code alone?
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2011-04-19 11:06 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-19 3:00 [PATCH 0/6] writeback: moving expire targets for background/kupdate works Wu Fengguang
2011-04-19 3:00 ` [PATCH 1/6] writeback: pass writeback_control down to move_expired_inodes() Wu Fengguang
2011-04-19 3:00 ` [PATCH 2/6] writeback: the kupdate expire timestamp should be a moving target Wu Fengguang
2011-04-19 7:02 ` Dave Chinner [this message]
2011-04-19 7:20 ` Wu Fengguang
2011-04-19 9:31 ` Jan Kara
2011-04-19 3:00 ` [PATCH 3/6] writeback: sync expired inodes first in background writeback Wu Fengguang
2011-04-19 7:35 ` Dave Chinner
2011-04-19 9:57 ` Jan Kara
2011-04-19 12:56 ` Wu Fengguang
2011-04-19 13:46 ` Wu Fengguang
2011-04-20 1:21 ` Dave Chinner
2011-04-20 2:53 ` Wu Fengguang
2011-04-21 0:45 ` Dave Chinner
2011-04-21 2:06 ` Wu Fengguang
2011-04-21 3:01 ` Dave Chinner
2011-04-21 3:59 ` Wu Fengguang
2011-04-21 4:10 ` Wu Fengguang
2011-04-21 4:36 ` Christoph Hellwig
2011-04-21 6:36 ` Dave Chinner
2011-04-21 16:04 ` Jan Kara
2011-04-22 2:24 ` Wu Fengguang
2011-04-22 21:12 ` Jan Kara
2011-04-26 5:37 ` Wu Fengguang
2011-04-26 14:30 ` Jan Kara
2011-04-20 7:38 ` Wu Fengguang
2011-04-21 1:01 ` Dave Chinner
2011-04-21 1:47 ` Wu Fengguang
2011-04-19 3:00 ` [PATCH 4/6] writeback: introduce writeback_control.inodes_cleaned Wu Fengguang
2011-04-19 9:47 ` Jan Kara
2011-04-19 3:00 ` [PATCH 5/6] writeback: try more writeback as long as something was written Wu Fengguang
2011-04-19 10:20 ` Jan Kara
2011-04-19 11:16 ` Wu Fengguang
2011-04-19 21:10 ` Jan Kara
2011-04-20 7:50 ` Wu Fengguang
2011-04-20 15:22 ` Jan Kara
2011-04-21 3:33 ` Wu Fengguang
2011-04-21 4:39 ` Christoph Hellwig
2011-04-21 6:05 ` Wu Fengguang
2011-04-21 16:41 ` Jan Kara
2011-04-22 2:32 ` Wu Fengguang
2011-04-22 21:23 ` Jan Kara
2011-04-21 7:09 ` Dave Chinner
2011-04-21 7:14 ` Christoph Hellwig
2011-04-21 7:52 ` Dave Chinner
2011-04-21 8:00 ` Christoph Hellwig
2011-04-19 3:00 ` [PATCH 6/6] NFS: return -EAGAIN when skipped commit in nfs_commit_unstable_pages() Wu Fengguang
2011-04-19 3:29 ` Trond Myklebust
2011-04-19 3:55 ` Wu Fengguang
2011-04-21 4:40 ` Christoph Hellwig
2011-04-19 6:38 ` [PATCH 0/6] writeback: moving expire targets for background/kupdate works Dave Chinner
2011-04-19 8:02 ` Wu Fengguang
2011-04-21 4:34 ` Christoph Hellwig
2011-04-21 5:50 ` Wu Fengguang
2011-04-21 5:56 ` Christoph Hellwig
2011-04-21 6:07 ` Wu Fengguang
2011-04-21 7:17 ` Christoph Hellwig
2011-04-21 10:15 ` Wu Fengguang
-- strict thread matches above, loose matches on Subject: below --
2010-07-22 5:09 [PATCH 0/6] [RFC] writeback: try to write older pages first Wu Fengguang
2010-07-22 5:09 ` [PATCH 2/6] writeback: the kupdate expire timestamp should be a moving target Wu Fengguang
2010-07-23 18:17 ` Jan Kara
2010-07-26 10:52 ` Mel Gorman
2010-07-26 11:32 ` Wu Fengguang
2010-08-01 15:29 ` Minchan Kim
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