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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E62AEC433EF for ; Mon, 18 Oct 2021 14:25:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8A9B60F8F for ; Mon, 18 Oct 2021 14:25:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231920AbhJRO1P (ORCPT ); Mon, 18 Oct 2021 10:27:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229833AbhJRO1P (ORCPT ); Mon, 18 Oct 2021 10:27:15 -0400 X-Greylist: delayed 341 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Mon, 18 Oct 2021 07:25:04 PDT Received: from gardel.0pointer.net (gardel.0pointer.net [IPv6:2a01:238:43ed:c300:10c3:bcf3:3266:da74]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47E61C06161C for ; Mon, 18 Oct 2021 07:25:04 -0700 (PDT) Received: from gardel-login.0pointer.net (gardel-mail [IPv6:2a01:238:43ed:c300:10c3:bcf3:3266:da74]) by gardel.0pointer.net (Postfix) with ESMTP id 7AA06E809E1; Mon, 18 Oct 2021 16:19:21 +0200 (CEST) Received: by gardel-login.0pointer.net (Postfix, from userid 1000) id 0C15A160DBD; Mon, 18 Oct 2021 16:19:20 +0200 (CEST) Date: Mon, 18 Oct 2021 16:19:20 +0200 From: Lennart Poettering To: Christoph Hellwig , Jens Axboe , Ming Lei , Martijn Coenen Cc: linux-block@vger.kernel.org, Luca Boccassi , Karel Zak Subject: Is LO_FLAGS_DIRECT_IO by default a good idea? Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org eMing, Christoph, Jens! Ming, 5 years ago or so you added support for dio/aio for the loopback block device, i.e. LO_FLAGS_DIRECT_IO. As I understood it's supposed to improve performance of loopback block devices substantially. I noticed that there's various software that enables it by default (Android, Docker), but a lot of other candidates currently do not (util-linux, Ubuntu Snaps, various systemd tools). We recently got a request to enable it by default in systemd, but information is scarce on the precise effect of enabling this, and whether there are any drawbacks. So my question really is just: is this a flag we should all just enable by default? Is there any reason not to enable it? Should util-linux' losetup defaults be changed regarding this? A brief answer like "yes, please, enable by default" would already make me happy. Thank you, Lennart -- Lennart Poettering, Berlin