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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 D1C2AC67863 for ; Mon, 22 Oct 2018 09:01:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88C8920652 for ; Mon, 22 Oct 2018 09:01:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88C8920652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728041AbeJVRSh (ORCPT ); Mon, 22 Oct 2018 13:18:37 -0400 Received: from verein.lst.de ([213.95.11.211]:35103 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727723AbeJVRSh (ORCPT ); Mon, 22 Oct 2018 13:18:37 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id 8242168BE1; Mon, 22 Oct 2018 11:00:58 +0200 (CEST) Date: Mon, 22 Oct 2018 11:00:58 +0200 From: Christoph Hellwig To: Jianchao Wang Cc: axboe@kernel.dk, martin.petersen@oracle.com, tom.leiming@gmail.com, hch@lst.de, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] block: fix the DISCARD request merge Message-ID: <20181022090058.GF18755@lst.de> References: <1540045777-10290-1-git-send-email-jianchao.w.wang@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1540045777-10290-1-git-send-email-jianchao.w.wang@oracle.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote: > There are two cases when handle DISCARD merge > - max_discard_segments == 1 > bios need to be contiguous > - max_discard_segments > 1 > Only nvme right now. It takes every bio as a range and different > range needn't to be contiguous. > > But now, attempt_merge screws this up. It always consider contiguity > for DISCARD for the case max_discard_segments > 1 and cannot merge > contiguous DISCARD for the case max_discard_segments == 1, because > rq_attempt_discard_merge always returns false in this case. > This patch fixes both of the two cases above. > > Signed-off-by: Jianchao Wang > --- > > V2: > - Add max_discard_segments > 1 checking in attempt_merge > - Change patch title and comment > - Add more comment in attempt_merge > > block/blk-merge.c | 24 +++++++++++++++++++----- > 1 file changed, 19 insertions(+), 5 deletions(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index 42a4674..8f22374 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q, > /* > * not contiguous > */ > - if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) > - return NULL; > + if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) { > + /* > + * When max_discard_segments is bigger than 1 (only nvme right > + * now), needn't consider the contiguity. > + */ > + if (!(req_op(req) == REQ_OP_DISCARD && > + queue_max_discard_segments(q) > 1)) > + return NULL; Why not: if (req_op(req) != REQ_OP_DISCARD || queue_max_discard_segments(q) == 1) which would be a lot more obvious? > + * counts here. > + * Two cases of Handling DISCARD: > + * - max_discard_segments == 1 > + * The bios need to be contiguous. > + * - max_discard_segments > 1 > + * Only nvme right now. It takes every bio as a > + * range and send them to controller together. The ranges > + * needn't to be contiguous. The formatting looks odd. Also I don't think we should mention the users here, as others might grow (virtio is in the pipe, SCSI could be supported easily if someone did the work).