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=-11.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 03DAEC4320A for ; Sat, 14 Aug 2021 08:57:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC20260F46 for ; Sat, 14 Aug 2021 08:57:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237587AbhHNI5w (ORCPT ); Sat, 14 Aug 2021 04:57:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:33942 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237543AbhHNI5v (ORCPT ); Sat, 14 Aug 2021 04:57:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628931442; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hVaGgxPnEuUaeVNs1e3S9yjlL7gUklGWzlvGDXZIRvc=; b=efYTrMuNZpbF8h40ieJd6aax+8kQd51t2ZXzvIXYt6HDt0GlSIa0cH6PCfbENggOubj/p9 lrLcKo7UH6FFOI/rn8FaBW0yqU997H0mEGXwmejAtSy1KX5/a8+Fgn02y1FmDFK27WEXtk y8ybfmGGELPqoL1jNIsXHjTsWU5pHwE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-313-kmYA8s_vNyajXmJosHO4ow-1; Sat, 14 Aug 2021 04:57:21 -0400 X-MC-Unique: kmYA8s_vNyajXmJosHO4ow-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 82B4D1853025; Sat, 14 Aug 2021 08:57:19 +0000 (UTC) Received: from T590 (ovpn-8-25.pek2.redhat.com [10.72.8.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 60F2818A77; Sat, 14 Aug 2021 08:57:10 +0000 (UTC) Date: Sat, 14 Aug 2021 16:57:06 +0800 From: Ming Lei To: Christoph Hellwig Cc: Guoqing Jiang , song@kernel.org, linux-raid@vger.kernel.org, jens@chianterastutte.eu, linux-block@vger.kernel.org Subject: Re: [PATCH] raid1: ensure bio doesn't have more than BIO_MAX_VECS sectors Message-ID: References: <20210813060510.3545109-1-guoqing.jiang@linux.dev> <0eac4589-ffd2-fb1a-43cc-87722731438a@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Sat, Aug 14, 2021 at 08:55:21AM +0100, Christoph Hellwig wrote: > On Fri, Aug 13, 2021 at 04:38:59PM +0800, Guoqing Jiang wrote: > > > > Ok, thanks. > > > > > In general the size of a bio only depends on the number of vectors, not > > > the total I/O size. But alloc_behind_master_bio allocates new backing > > > pages using order 0 allocations, so in this exceptional case the total > > > size oes actually matter. > > > > > > While we're at it: this huge memory allocation looks really deadlock > > > prone. > > > > Hmm, let me think more about it, or could you share your thought? ???? > > Well, you'd need a mempool which can fit the max payload of a bio, > that is BIO_MAX_VECS pages. > > FYI, this is what I'd do instead of this patch for now. We don't really > need a vetor per sector, just per page. So this limits the I/O > size a little less. > > diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c > index 3c44c4bb40fc..5b27d995302e 100644 > --- a/drivers/md/raid1.c > +++ b/drivers/md/raid1.c > @@ -1454,6 +1454,15 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio, > goto retry_write; > } > > + /* > + * When using a bitmap, we may call alloc_behind_master_bio below. > + * alloc_behind_master_bio allocates a copy of the data payload a page > + * at a time and thus needs a new bio that can fit the whole payload > + * this bio in page sized chunks. > + */ > + if (bitmap) > + max_sectors = min_t(int, max_sectors, BIO_MAX_VECS * PAGE_SIZE); s/PAGE_SIZE/PAGE_SECTORS > + > if (max_sectors < bio_sectors(bio)) { > struct bio *split = bio_split(bio, max_sectors, > GFP_NOIO, &conf->bio_split); > Here the limit is max single-page vectors, and the above way may not work, such as: 0 ~ 254: each bvec's length is 512 255: bvec's length is 8192 the total length is just 512*255 + 8192 = 138752 bytes = 271 sectors, but it still may need 257 bvecs, which can't be allocated via bio_alloc_bioset(). One solution is to add queue limit of max_single_page_bvec, and let blk_queue_split() handle it. Thanks, Ming