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[68.160.176.52]) by smtp.gmail.com with ESMTPSA id o21sm5295158qta.89.2022.01.10.11.26.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Jan 2022 11:26:30 -0800 (PST) Date: Mon, 10 Jan 2022 14:26:29 -0500 From: Mike Snitzer To: Ming Lei Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, dm-devel@redhat.com Subject: Re: [PATCH 0/3] blk-mq/dm-rq: support BLK_MQ_F_BLOCKING for dm-rq Message-ID: References: <20211221141459.1368176-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Dec 28 2021 at 4:30P -0500, Mike Snitzer wrote: > On Wed, Dec 22 2021 at 11:16P -0500, > Ming Lei 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