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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 E9D47C35240 for ; Fri, 31 Jan 2020 06:42:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C08E821734 for ; Fri, 31 Jan 2020 06:42:32 +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="mbwTRV+J" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726023AbgAaGmc (ORCPT ); Fri, 31 Jan 2020 01:42:32 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:53334 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725832AbgAaGmb (ORCPT ); Fri, 31 Jan 2020 01:42:31 -0500 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=4RziqBNwPU1PXyuUYR4uTQ9MUQMUjgsmxUEvgGf8uVg=; b=mbwTRV+JFE7kOQ/Zc1q7EWWLo b/r6VaG5PA2zFHi4pvVcHg00QQM2cM663Xq1D41XOwf0UQdQdBNI2xvUvvuRWZc0z3F9LIYg5uvSB Od2BHuooTiRfcTGuydXKRdUSEgl6XNVJsSYSUM37WQMbf/wb7XNSVQDdHWL3GqkwTsluhlPKhw6S/ EP3EB4/pADxjzTK6JdQpS2tIBSbJEw8Ly4vzgw/v+FJrXluZhHIuqgyn0eOfaxQ3TI9XX6banLZW8 zNWG9hIz5ggAbgKPzcd24gpk7VbDWT32ozJTEJsOQql+384AXzT7RsS4uJWfpkFJ7BZl+lVgNVI5k PbQlk0vAw==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1ixQ0c-0000EL-Oy; Fri, 31 Jan 2020 06:42:30 +0000 Date: Thu, 30 Jan 2020 22:42:30 -0800 From: Christoph Hellwig To: Bijan Mottahedeh Cc: axboe@kernel.dk, linux-block@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [PATCH 1/1] block: Manage bio references so the bio persists until necessary Message-ID: <20200131064230.GA28151@infradead.org> References: <1580441022-59129-1-git-send-email-bijan.mottahedeh@oracle.com> <1580441022-59129-2-git-send-email-bijan.mottahedeh@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1580441022-59129-2-git-send-email-bijan.mottahedeh@oracle.com> 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 On Thu, Jan 30, 2020 at 07:23:42PM -0800, Bijan Mottahedeh wrote: > Get a reference to a bio, so it won't be freed if end_io() gets to > it before submit_io() returns. Defer the release of the first bio > in a mult-bio request until the last end_io() since the first bio is > embedded in the dio structure and must therefore persist through an > entire multi-bio request. Can you explain the issue a little more? The initial bio is embedded into the dio, and will have a reference until the bio_put call at the end of the function, so we can't have a race for that one and won't ever need the refcount for the single bio case. Avoiding the atomic is pretty important for aio/uring performance.