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=-6.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 A8DF6C432C3 for ; Tue, 9 Feb 2021 21:21:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7AC0664E8B for ; Tue, 9 Feb 2021 21:21:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234412AbhBIVU5 (ORCPT ); Tue, 9 Feb 2021 16:20:57 -0500 Received: from mail.kernel.org ([198.145.29.99]:46556 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234284AbhBIVMp (ORCPT ); Tue, 9 Feb 2021 16:12:45 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 94F4864E85; Tue, 9 Feb 2021 19:55:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1612900543; bh=/VVBW/mmIaA9aKxI4f8SyqvwmyZqliL2BhQwvcCvZfA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=HsE/Kxij+DWxv152OJJcn+tRfjMZQ74BZ/MkOBURXxcAOGGHo+C4qd44rbRSwWhzh 2YSwczO9yPWYBGDK+li9B2xVV7d0GVnbiuIxDvH9bkQzGbBdEx7BEru5t6O+6Ck1Hb V368P9hl5NY4qebU5s1QtbZ59vFE2LzjOXzGH6nU= Date: Tue, 9 Feb 2021 11:55:42 -0800 From: Andrew Morton To: Jens Axboe Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@infradead.org Subject: Re: [PATCHSET v2 0/3] Improve IOCB_NOWAIT O_DIRECT reads Message-Id: <20210209115542.3e407e306a4f1af29257c8f6@linux-foundation.org> In-Reply-To: <20210209023008.76263-1-axboe@kernel.dk> References: <20210209023008.76263-1-axboe@kernel.dk> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, 8 Feb 2021 19:30:05 -0700 Jens Axboe wrote: > Hi, > > For v1, see: > > https://lore.kernel.org/linux-fsdevel/20210208221829.17247-1-axboe@kernel.dk/ > > tldr; don't -EAGAIN IOCB_NOWAIT dio reads just because we have page cache > entries for the given range. This causes unnecessary work from the callers > side, when the IO could have been issued totally fine without blocking on > writeback when there is none. > Seems a good idea. Obviously we'll do more work in the case where some writeback needs doing, but we'll be doing synchronous writeout in that case anyway so who cares. Please remind me what prevents pages from becoming dirty during or immediately after the filemap_range_needs_writeback() check? Perhaps filemap_range_needs_writeback() could have a comment explaining what it is that keeps its return value true after it has returned it!