From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A4BAC2D0CE for ; Tue, 21 Jan 2020 15:14:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1407D2253D for ; Tue, 21 Jan 2020 15:14:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728811AbgAUPOT (ORCPT ); Tue, 21 Jan 2020 10:14:19 -0500 Received: from relay.sw.ru ([185.231.240.75]:40918 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727059AbgAUPOT (ORCPT ); Tue, 21 Jan 2020 10:14:19 -0500 Received: from dhcp-172-16-24-104.sw.ru ([172.16.24.104]) by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1itvDk-0001Vx-Rr; Tue, 21 Jan 2020 18:13:37 +0300 Subject: Re: [PATCH v4 6/7] dm: Directly disable max_allocate_sectors for now To: Mike Snitzer Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, martin.petersen@oracle.com, bob.liu@oracle.com, axboe@kernel.dk, agk@redhat.com, dm-devel@redhat.com, song@kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, Chaitanya.Kulkarni@wdc.com, darrick.wong@oracle.com, ming.lei@redhat.com, osandov@fb.com, jthumshirn@suse.de, minwoo.im.dev@gmail.com, damien.lemoal@wdc.com, andrea.parri@amarulasolutions.com, hare@suse.com, tj@kernel.org, ajay.joshi@wdc.com, sagi@grimberg.me, dsterba@suse.com, bvanassche@acm.org, dhowells@redhat.com, asml.silence@gmail.com References: <157960325642.108120.13626623438131044304.stgit@localhost.localdomain> <157960337238.108120.18048939587162465175.stgit@localhost.localdomain> <20200121122458.GA9365@redhat.com> <619a7a14-44e6-eca7-c1ea-3f04abeee53d@virtuozzo.com> <20200121134840.GA9944@redhat.com> <20200121144310.GA10055@redhat.com> From: Kirill Tkhai Message-ID: <2b393b74-952e-10ff-9f2c-4ea19cf74f88@virtuozzo.com> Date: Tue, 21 Jan 2020 18:13:36 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200121144310.GA10055@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 21.01.2020 17:43, Mike Snitzer wrote: > On Tue, Jan 21 2020 at 9:20am -0500, > Kirill Tkhai wrote: > >> On 21.01.2020 16:48, Mike Snitzer wrote: >>> On Tue, Jan 21 2020 at 8:33am -0500, >>> Kirill Tkhai wrote: >>> >>>> On 21.01.2020 15:36, Kirill Tkhai wrote: >>>>> On 21.01.2020 15:24, Mike Snitzer wrote: >>>>>> On Tue, Jan 21 2020 at 5:42am -0500, >>>>>> Kirill Tkhai wrote: >>>>>> >>>>>>> Since dm inherits limits from underlining block devices, >>>>>>> this patch directly disables max_allocate_sectors for dm >>>>>>> till full allocation support is implemented. >>>>>>> >>>>>>> This prevents high-level primitives (generic_make_request_checks(), >>>>>>> __blkdev_issue_write_zeroes(), ...) from sending REQ_ALLOCATE >>>>>>> requests. >>>>>>> >>>>>>> Signed-off-by: Kirill Tkhai >>>>>>> --- >>>>>>> drivers/md/dm-table.c | 2 ++ >>>>>>> drivers/md/md.h | 1 + >>>>>>> 2 files changed, 3 insertions(+) >>>>>> >>>>>> You're mixing DM and MD changes in the same patch. >>>>>> >>>>>> But I'm wondering if it might be best to set this default for stacking >>>>>> devices in blk_set_stacking_limits()? >>>>>> >>>>>> And then it is up to each stacking driver to override as needed. >>>>> >>>>> Hm. Sound like a good idea. This "lim->max_allocate_sectors = 0" in blk_set_stacking_limits() >>>>> should work for dm's dm_calculate_queue_limits(), since it calls blk_stack_limits(), which is: >>>>> >>>>> t->max_allocate_sectors = min(t->max_allocate_sectors, >>>>> b->max_allocate_sectors); >>>>> >>>>> Could you please tell is this fix is also enough for md? >>>> >>>> It looks like it's enough since queue defaults are set in md_alloc()->blk_set_stacking_limits(). >>>> In case of we set "max_allocate_sectors = 0", in further it can be changed only manually, >>>> but nobody does this. >>> >>> Yes, it will work to disable this capability for MD and DM. >>> >>> But if/when a stacked device _dooes_ want to support this then it'll be >>> awkward to override this stacking default to allow blk_stack_limits() >>> to properly stack up this limit. blk_limits are extremely fiddley so >>> this isn't necessarily new. But by explicitly defaulting to 0 and then >>> having blk_stack_limits use min() for this limit: it results in stacking >>> drivers needing to clumsily unwind the default. E.g. DM will need to >>> tweak its blk_stack_limits() related code to allow override that >>> actually _does_ stack up the underlying devices' capability (and not >>> just impose its own limit that ignores the underlying devices). >>> >>> So I'm not convinced this is the right way to go (be it the v4 approach >>> you took or the cleaner use of blk_set_stacking_limits I suggested). >> >> Is there a strong vision about the way we should go? Or you leave this choose >> up to me? > > I don't have time to work through it at the moment (e.g. implementing > dm-thinp support to know what the block core code should be) so I'll > just defer to you on a disabling it for now. > >>> And to be clear, I'm interested in having DM thinp support this >>> capability to preallocate blocks. >> >> My opinion is it would be better to not mix several subsystem related >> support in a single patch set. Both of the approaches (v4 or that you >> suggested) do not prevents us to implement allocation support in next >> patch series. After we have the base functionality enabled, we may add >> support in other subsystems and drivers one by one with more focus >> on the subsystem specificities and with the best possible attention. > > Yeah, I'm aware nothing is ever set in stone. > > Setting to 0 in blk_set_stacking_limits() is OK for now. I get your point. Thanks for the suggestion and comments, Mike. Kirill