linux-kernel - Re: blk-mq flush fix

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Message-ID: <20131028084821.GA31270@infradead.org>
Date:	Mon, 28 Oct 2013 01:48:21 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Alexander Gordeev <agordeev@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	linux-kernel@...r.kernel.org
Subject: Re: blk-mq flush fix

On Sun, Oct 27, 2013 at 10:29:25PM +0000, Jens Axboe wrote:
> On Sat, Oct 26 2013, Christoph Hellwig wrote:
> > I think this variant of the patch from Alexander should fix the issue
> > in a minimally invasive way.  Longer term I'd prefer to use q->flush_rq
> > like in the non-mq case by copying over the context and tag information.
> 
> This one is pretty simple, we could definitely use it as a band aid. I
> too would greatly prefer using the static ->flush_rq instead. Just have
> it marked to bypass most of the free logic.

We already bypass the free logical by setting and end_io callback for
a while, similar to what the old code does.  Maybe it's not all that
hard to prealloc the request, let me give a sping.  Using the static
allocated one will be hard due to the driver-specific extra data,
though.

> I'll add this one.

Gimme another day or so to figure this out.
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