linux-kernel - blk_flush_plug in the MD code, was Re: [xfs-masters] linux-next: manual merge of the xfs tree with Linus' tree

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Message-ID: <20110330115738.GA16484@lst.de>
Date:	Wed, 30 Mar 2011 13:57:38 +0200
From:	Christoph Hellwig <hch@....de>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	neilb@...e.de
Subject: blk_flush_plug in the MD code, was Re: [xfs-masters] linux-next:
	manual merge of the xfs tree with Linus' tree

On Wed, Mar 30, 2011 at 01:43:55PM +0200, Jens Axboe wrote:
> On 2011-03-29 22:08, Christoph Hellwig wrote:
> > FYI, the blk_flush_plug call in ufs_truncate also seem to be almost
> > certainly incorrect as it's followed by a yield.
> > 
> > That only leaves the RAID code as remaining modular users of it, and
> > I suspect it really is something that shouldn't need to be exported.
> 
> Agree, once things have settled down we can reap the remaining and keep
> it internal.

In fact I think the blk_flush_plug calls in the raid1/raid10 code can
simply be removed without a replacement.  They are in wait_even_loops
which schedule before/after the call so we do get the implicit context
switch plugs there.  Even more they are generally called from the
make_request handler, which for MD is in the loop around
__generic_make_request and thus can't actually unplug in a sensible
way.
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