From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: block: flush queued bios when the process blocks Date: Tue, 27 May 2014 12:56:57 -0700 Message-ID: <20140527195657.GE2276@kmo> References: <5384AA79.4010206@kernel.dk> <5384B26D.1000703@kernel.dk> <20140527173306.GA12201@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140527173306.GA12201@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: Mikulas Patocka , Jens Axboe , linux-kernel@vger.kernel.org, dm-devel@redhat.com, "Alasdair G. Kergon" List-Id: dm-devel.ids On Tue, May 27, 2014 at 01:33:06PM -0400, Mike Snitzer wrote: > On Tue, May 27 2014 at 12:26pm -0400, > Mikulas Patocka wrote: > > > On Tue, 27 May 2014, Jens Axboe wrote: > > > > > On 2014-05-27 09:23, Mikulas Patocka wrote: > > > > > > > The patch adds bio list flushing to the scheduler just besides plug > > > > flushsing. > > > > > > ... which is exactly why I'm commenting. It'd be great to avoid yet one more > > > scheduler hook for this sort of thing. > > > > > > -- > > > Jens Axboe > > > > One could create something like schedule notifier chain, but I'm not sure > > if it is worth the complexity because of just two users. If more users > > come in the future, it could be generalized. > > It could be that Jens is suggesting updating blk_needs_flush_plug() and > blk_schedule_flush_plug() to be bio_list aware too (rather than train > sched_submit_work() from this new bio_list)? > > Somewhat awkward, but _could_ be made to work. No... I started on this ages and ages ago, but the patches were nowhere near ready to go out. What I'd do is rework the existing blk_plug to work in terms of bios, not requests. This is a fair amount of work, and then make_request_fn() needs to be able to take multiple bios at a time, but IIRC there were other simplifications that fell out of this and this also means bio based drivers can take advantage of plugging/batching. Once this is done, you just... replace the bio list in generic_make_request() with a plug. Boom, done. (oh, and to avoid blowing the stack the scheduler/plug callback or whatever needs to check the current stack usage and punt off to a per request_queue workqueue, but that's easy enough).