From: Goldwyn Rodrigues Subject: Re: [PATCH 5/8] nowait aio: return on congested block device Date: Wed, 8 Mar 2017 20:18:54 -0600 Message-ID: <310c6725-3263-2790-a445-d58e464fd3e4@suse.de> References: <20170228233610.25456-1-rgoldwyn@suse.de> <20170228233610.25456-6-rgoldwyn@suse.de> <0d1ba678-69c0-16ce-6c3e-475cd8da203c@grimberg.me> <44cc02b1-f7ac-cbc6-6f09-726ae8225358@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: hch@infradead.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, Goldwyn Rodrigues To: Jens Axboe , Sagi Grimberg , jack@suse.com Return-path: In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 03/08/2017 10:17 AM, Jens Axboe wrote: > On 03/08/2017 08:00 AM, Goldwyn Rodrigues wrote: >> >> >> On 03/08/2017 01:03 AM, Sagi Grimberg wrote: >>> >>>> - if (likely(blk_queue_enter(q, false) == 0)) { >>>> + if (likely(blk_queue_enter(q, bio_flagged(bio, BIO_NOWAIT)) >>>> == 0)) { >>>> ret = q->make_request_fn(q, bio); >>> >>> I think that for ->make_request to not block we'd need to set >>> BLK_MQ_REQ_NOWAIT in blk_mq_alloc_data to avoid blocking on a tag >>> allocation. >>> >>> Something like the untested addition below: >> >> I did that in the first series, but there are too many reasons to block >> in blk-mq [1]. I dropped blk-mq work in v2. > > That's complete nonsense, there are no more places in blk-mq that will > block that in the legacy path. Most of the examples from your URL: > >> [1] https://patchwork.kernel.org/patch/9571051/ > > are not blk-mq, but writeback throttling, and drivers that explicitly > hook into ->make_request_fn. > > As others have mentioned, it's a total non-starter to focus on the > deprecated IO path and just ignore the new one. Back to the drawing > board. > Thanks, I understood what I was doing wrong. I will include blk-mq in the patch. -- Goldwyn