linux-kernel - Re: [PATCH 0/7] writeback: avoid touching dirtied

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Date:	Sat, 22 Oct 2011 13:38:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] writeback: avoid touching dirtied_when on blocked
 inodes

On Sat, Oct 22, 2011 at 11:11:35AM +0800, Wu Fengguang wrote:
> > > btw, with the I_SYNC case converted, it's actually no longer necessary
> > > to keep a standalone b_more_io_wait. It should still be better to keep
> > > the list and the above error check for catching possible errors and
> > > the flexibility of adding policies like "don't retry possible blocked
> > > inodes in N seconds as long as there are other inodes to work with".
> > > 
> > > The below diff only intends to show the _possibility_ to remove
> > > b_more_io_wait:
> >   Good observation. So should we introduce b_more_io_wait in the end? We
> > could always introduce it when the need for some more complicated policy
> > comes...
> > 
> 
> I have no problem removing it if you liked it more. Anyway, let me
> test the idea out first (just kicked off the tests).

When removing b_more_io_wait, performance is slightly dropped
comparing to the full more_io_wait patchset.

3.1.0-rc9-ioless-full-more_io_wait-next-20111014+  3.1.0-rc9-ioless-full-more_io_wait-x-next-20111014+  
------------------------  ------------------------  
                   45.30        +6.3%        48.14  thresh=1G/ext3-1dd-4k-8p-4096M-1024M:10-X
                   48.23        -2.0%        47.27  thresh=1G/ext4-100dd-4k-8p-4096M-1024M:10-X
                   54.21        -2.6%        52.80  thresh=1G/ext4-10dd-4k-8p-4096M-1024M:10-X
                   56.07        -0.3%        55.91  thresh=1G/ext4-1dd-4k-8p-4096M-1024M:10-X
                   45.12        -5.8%        42.49  thresh=1G/xfs-100dd-4k-8p-4096M-1024M:10-X
                   53.94        -1.2%        53.27  thresh=1G/xfs-10dd-4k-8p-4096M-1024M:10-X
                   55.66        -0.1%        55.63  thresh=1G/xfs-1dd-4k-8p-4096M-1024M:10-X
                  358.53        -0.8%       355.51  TOTAL write_bw

I'll try to reduce the changes and retest.

In general it looks better we first root case the "decreasing wrote
pages by writeback_single_inode() over time" problem before looking
into further steps..

Thanks,
Fengguang
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