linux-kernel - Re: [RESEND][PATCH v2] block: remove plugging at buffered write time

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Message-Id: <20120411161344.309f12ef.akpm@linux-foundation.org>
Date:	Wed, 11 Apr 2012 16:13:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
	Chris Mason <chris.mason@...cle.com>,
	Shaohua Li <shli@...ionio.com>
Subject: Re: [RESEND][PATCH v2] block: remove plugging at buffered write
 time

On Mon, 09 Apr 2012 10:34:44 -0400
Jeff Moyer <jmoyer@...hat.com> wrote:

> Wu Fengguang <fengguang.wu@...el.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.
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