From: Sagi Grimberg Subject: Re: [PATCH 5/8] nowait aio: return on congested block device Date: Wed, 8 Mar 2017 09:03:08 +0200 Message-ID: <0d1ba678-69c0-16ce-6c3e-475cd8da203c@grimberg.me> References: <20170228233610.25456-1-rgoldwyn@suse.de> <20170228233610.25456-6-rgoldwyn@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed 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: Goldwyn Rodrigues , jack@suse.com Return-path: Received: from mail-wm0-f68.google.com ([74.125.82.68]:34926 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751226AbdCHHFW (ORCPT ); Wed, 8 Mar 2017 02:05:22 -0500 In-Reply-To: <20170228233610.25456-6-rgoldwyn@suse.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: > - 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: -- diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 09af8ff18719..40e78b57fb44 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -119,6 +119,9 @@ struct request *blk_mq_sched_get_request(struct request_queue *q, if (likely(!data->hctx)) data->hctx = blk_mq_map_queue(q, data->ctx->cpu); + if (likely(bio) && bio_flagged(bio, BIO_NOWAIT)) + data->flags |= BLK_MQ_REQ_NOWAIT; + if (e) { data->flags |= BLK_MQ_REQ_INTERNAL; --