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=-5.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 2DC49CA9EAE for ; Tue, 29 Oct 2019 11:04:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F381E214B2 for ; Tue, 29 Oct 2019 11:04:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ld/JXI5Z" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726099AbfJ2LE2 (ORCPT ); Tue, 29 Oct 2019 07:04:28 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:49982 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725776AbfJ2LE2 (ORCPT ); Tue, 29 Oct 2019 07:04:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=1ZbSp1CPL1cN9bi6Y9K+vpaW0lBwJnmkUNhvWg9tzjs=; b=Ld/JXI5ZJayM4AljENdLIke5G OOfKWI2qFEGEdflRVLCCx4tigevR6zkw3gco5hLBdqx2sIENBwvy/Rmtx1JF/3/mtz1XH7ba4fQEv +BpJMN6MW/X3vjjfEwX1xsmHv1YV7+pM7Ts2/NDKK4tmGZYJHmRoKK8SoMT6U9pvZnP/2zhkaDHU9 noC1Ph/Yjm0je2aVrwgobtEyV5N5Ftrz6bN5tVT9hzJh+CYyvtEFAQObGJw8UNSdYI00PGNN36kJi LswI1+rIyTMOg6OqPppO8DGTlepaAeuftobg8zua6a0eP+doVsegGD04NOuG2Ng2GqByOW7l3Ah3A 1AxTQAT+A==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1iPPIX-0004jT-PL; Tue, 29 Oct 2019 11:04:25 +0000 Date: Tue, 29 Oct 2019 04:04:25 -0700 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Coly Li , Christoph Hellwig , Keith Busch , linux-bcache@vger.kernel.org Subject: Re: [PATCH V3] block: optimize for small block size IO Message-ID: <20191029110425.GA4382@infradead.org> References: <20191029105125.12928-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191029105125.12928-1-ming.lei@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org I still haven't seen an explanation why this simple thing doesn't work just as well: diff --git a/block/blk-merge.c b/block/blk-merge.c index 48e6725b32ee..f3073700166f 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -309,6 +309,11 @@ void __blk_queue_split(struct request_queue *q, struct bio **bio, nr_segs); break; default: + if ((*bio)->bi_vcnt == 1 && + (*bio)->bi_io_vec[0].bv_len <= PAGE_SIZE) { + *nr_segs = 1; + return; + } split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs); break; }