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From: Mike Snitzer <snitzer@redhat.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	Jens Axboe <axboe@kernel.dk>,
	dm-devel@redhat.com, linux-block@vger.kernel.org
Subject: Re: [dm-devel] [PATCH 0/3] blk-mq/dm-rq: support BLK_MQ_F_BLOCKING for dm-rq
Date: Mon, 10 Jan 2022 14:26:29 -0500	[thread overview]
Message-ID: <YdyIZR4LkQTVjhWf@redhat.com> (raw)
In-Reply-To: <YcuB4K8P2d9WFb83@redhat.com>

On Tue, Dec 28 2021 at  4:30P -0500,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Wed, Dec 22 2021 at 11:16P -0500,
> Ming Lei <ming.lei@redhat.com> wrote:
> 
> > On Tue, Dec 21, 2021 at 08:21:39AM -0800, Christoph Hellwig wrote:
> > > On Tue, Dec 21, 2021 at 10:14:56PM +0800, Ming Lei wrote:
> > > > Hello,
> > > > 
> > > > dm-rq may be built on blk-mq device which marks BLK_MQ_F_BLOCKING, so
> > > > dm_mq_queue_rq() may become to sleep current context.
> > > > 
> > > > Fixes the issue by allowing dm-rq to set BLK_MQ_F_BLOCKING in case that
> > > > any underlying queue is marked as BLK_MQ_F_BLOCKING.
> > > > 
> > > > DM request queue is allocated before allocating tagset, this way is a
> > > > bit special, so we need to pre-allocate srcu payload, then use the queue
> > > > flag of QUEUE_FLAG_BLOCKING for locking dispatch.
> > > 
> > > What is the benefit over just forcing bio-based dm-mpath for these
> > > devices?
> > 
> > At least IO scheduler can't be used for bio based dm-mpath, also there should
> > be other drawbacks for bio based mpath and request mpath is often the default
> > option, maybe Mike has more input about bio vs request dm-mpath.
> 
> Yeah, people use request-based for IO scheduling and more capable path
> selectors. Imposing bio-based would be a pretty jarring workaround for 
> BLK_MQ_F_BLOCKING. request-based DM should properly support it.
> 
> I'm on vacation for the next week but will have a look at this
> patchset once I'm back.

I replied last week and hoped Jens would pick this patchset up after
my Reviewed-by of patch 3/3.

Christoph wasn't back though, so best to kick this thread again.

Thoughts on this patchset?

Thanks,
Mike

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  reply	other threads:[~2022-01-10 19:26 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-21 14:14 [dm-devel] [PATCH 0/3] blk-mq/dm-rq: support BLK_MQ_F_BLOCKING for dm-rq Ming Lei
2021-12-21 14:14 ` [dm-devel] [PATCH 1/3] block: split having srcu from queue blocking Ming Lei
2022-01-11 18:13   ` Jeff Moyer
2021-12-21 14:14 ` [dm-devel] [PATCH 2/3] block: add blk_alloc_disk_srcu Ming Lei
2022-01-11 18:13   ` Jeff Moyer
2021-12-21 14:14 ` [dm-devel] [PATCH 3/3] dm: mark dm queue as blocking if any underlying is blocking Ming Lei
2022-01-06 15:40   ` Mike Snitzer
2022-01-06 15:51     ` Ming Lei
2022-01-10 19:23       ` Mike Snitzer
2022-01-11 18:14   ` Jeff Moyer
2021-12-21 16:21 ` [dm-devel] [PATCH 0/3] blk-mq/dm-rq: support BLK_MQ_F_BLOCKING for dm-rq Christoph Hellwig
2021-12-23  4:16   ` Ming Lei
2021-12-28 21:30     ` Mike Snitzer
2022-01-10 19:26       ` Mike Snitzer [this message]
2022-01-11  8:34       ` Christoph Hellwig
2022-01-11 16:15         ` Mike Snitzer
2022-01-17  8:08           ` Christoph Hellwig
2022-01-11 18:23         ` Jeff Moyer
2022-01-17  8:10           ` Christoph Hellwig
2022-01-19 21:03             ` Mike Snitzer

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