From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: [PATCH] block: flush queued bios when the process blocks Date: Tue, 27 May 2014 13:06:00 -0700 Message-ID: <20140527200600.GG2276@kmo> References: <5384AA79.4010206@kernel.dk> <5384B26D.1000703@kernel.dk> <5384CE82.90601@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Mikulas Patocka Cc: Jens Axboe , linux-kernel@vger.kernel.org, dm-devel@redhat.com, "Alasdair G. Kergon" , Mike Snitzer List-Id: dm-devel.ids On Tue, May 27, 2014 at 03:56:00PM -0400, Mikulas Patocka wrote: > > > On Tue, 27 May 2014, Jens Axboe wrote: > > > On 2014-05-27 10:26, 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. > > > > Except such a thing already exists, there are unplug callback chains. All I'm > > asking is that you look into how feasible it would be to use something like > > that, instead of reinventing the wheel. > > > > -- > > Jens Axboe > > Do you mean moving current->bio_list to struct blk_plug and calling > blk_start_plug/blk_finish_plug around generic_make_request? > > It would be possible on a condition that we can redirect all bios to a > workqueue (i.e. eliminate bio_kmalloc and always use bio_alloc_bioset). > > What are performance implications of this - does it make sense to have > blk_start_plug/blk_finish_plug around every call to generic_make_request? > - that means that all i/o requests will be added to a plug and then > unplugged. We've already got blk_start_plug() calls around IO submission at higher points in the stack. (I actually have seen it show up in profiles though, it probably would be worth inlining and slimming down a bit).