linux-kernel - Re: [PATCH] block: remove plugging at buffered write time

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Message-ID: <20120209183027.GT8384@shiny>
Date:	Thu, 9 Feb 2012 13:30:27 -0500
From:	Chris Mason <chris.mason@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Li Shaohua <shaohua.li@...el.com>
Subject: Re: [PATCH] block: remove plugging at buffered write time

On Thu, Feb 09, 2012 at 01:06:35PM -0500, Christoph Hellwig wrote:
> On Thu, Feb 09, 2012 at 04:02:24PM +0800, Wu Fengguang wrote:
> > On Thu, Feb 09, 2012 at 10:27:19AM +1100, Dave Chinner wrote:
> > > On Wed, Feb 08, 2012 at 07:01:44PM +0800, Wu Fengguang wrote:
> > > > Buffered write(2) is not directly tied to IO, so it's not suitable to
> > > > handle plug in generic_file_aio_write().
> > > 
> > > But generic_sync_write() does issue IO for O_SYNC writes, so unless
> > > there is plugging at a lower layer in the writeback code then it
> > > appears to me that plugging is still necessary (at least inside the
> > > sync branch)....
> > 
> > Good catch! It looks that generic_write_sync() eventually calls into
> > vfs_fsync_range() which further calls ->fsync(). We may add plugging
> > around it:
> 
> 
> NAK, please keep the plugging down in the fs, or the libraries used but
> not common VFS code.

Please, what Christoph said.  At least for btrfs plugging here is wrong.

-chris

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