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Re: [PATCH 0/2] Improve writeout pattern from xfs_flush_pages()

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 0/2] Improve writeout pattern from xfs_flush_pages()
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 4 Aug 2011 14:07:24 +0200
Cc: Jan Kara <jack@xxxxxxx>, xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
In-reply-to: <20110804104210.GA30823@xxxxxxxxxxxxx>
References: <1312404545-15400-1-git-send-email-jack@xxxxxxx> <20110803214206.GA20477@xxxxxxxxxxxxx> <20110804103616.GF17196@xxxxxxxxxxxxx> <20110804104210.GA30823@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu 04-08-11 06:42:10, Christoph Hellwig wrote:
> On Thu, Aug 04, 2011 at 12:36:16PM +0200, Jan Kara wrote:
> > > The first one actually is a synchronous writeout, just implemented in
> > > a rather odd way by doing the xfs_ioend_wait right after it, so your
> > > change is actively harmful for it.
> >   Oh, right. BTW cannot be truncate livelocked on a busy file because of
> > that xfs_ioend_wait()?
> 
> Not really.  We requite the iolock for new writes to start, and truncate
> holds it exclusively.  But I'm working on a series for 3.2 to remove
> xfs_ioend_wait and just rely on inode_dio_wait for direct I/O, so it
> will be gone soon.  At this point I'll also have to switch to
> filemap_write_and_wait_range for this caller.
> 
> > > The third one is opportunistic writeout if a file got truncated down on
> > > final release.  filemap_flush probably is fine here, but there's no need
> > > for a range version.  If you replace it with filemap_flush please also
> > > kill the useless wrapper while you're at it.
> >   Do you mean xfs_flush_pages()? OK, I can do that.
> 
> Yes, xfs_flush_pages should go - at least he async version and its
> abuse of the buffer flags.
  Hmm, BTW, shouldn't the call to xfs_flush_pages() in
xfs_file_buffered_aio_write() be converted to an asynchronous one? I don't
quite see a point in waiting for io completion... Generally, flushing of
the inode there seems of limited usefulness to me since that inode could be
just a tiny victim not holding much delayallocated blocks.

                                                                        Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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