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Date: Wed, 11 Apr 2012 16:13:44 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>, Jens Axboe <axboe@kernel.dk>,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>,
        Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>,
        Chris Mason <chris.mason@oracle.com>, Shaohua Li <shli@fusionio.com>
Subject: Re: [RESEND][PATCH v2] block: remove plugging at buffered write
 time
Message-Id: <20120411161344.309f12ef.akpm@linux-foundation.org>
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On Mon, 09 Apr 2012 10:34:44 -0400
Jeff Moyer <jmoyer@redhat.com> wrote:

> Wu Fengguang <fengguang.wu@intel.com> writes:
> 
> > Buffered write(2) is not directly tied to IO, so it's not suitable to
> > handle plug in generic_file_aio_write().
> [snip, moved]
> > Note that plugging for O_SYNC writes is also removed. The user may pass
> > arbitrary @size arguments, which may be much larger than the preferable
> > I/O size, or may cross extent/device boundaries. Let the lower layers
> > handle the plugging. Otherwise the plugging code here will turn the
> > low level plugging into no-ops.
> 
> I assume you have some numbers to back this up, right?  Care to share
> those?

Yes please.

We've broken this stuff a few times recently - we should review and
test carefully.

> > Also moves unplugging for direct I/O from around ->direct_IO() down to
> > do_blockdev_direct_IO().
> 
> This could be handled in a separate patch.

I think that would be better.