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=-0.8 required=3.0 tests=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 35EC5C43331 for ; Thu, 26 Mar 2020 18:22:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1240A20719 for ; Thu, 26 Mar 2020 18:22:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727822AbgCZSWT (ORCPT ); Thu, 26 Mar 2020 14:22:19 -0400 Received: from mail.itouring.de ([188.40.134.68]:52700 "EHLO mail.itouring.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727446AbgCZSWT (ORCPT ); Thu, 26 Mar 2020 14:22:19 -0400 Received: from tux.applied-asynchrony.com (p5B07E2B3.dip0.t-ipconnect.de [91.7.226.179]) by mail.itouring.de (Postfix) with ESMTPSA id 9B625416B3B8 for ; Thu, 26 Mar 2020 19:22:17 +0100 (CET) Received: from [192.168.100.223] (ragnarok.applied-asynchrony.com [192.168.100.223]) by tux.applied-asynchrony.com (Postfix) with ESMTP id 647E0F01604 for ; Thu, 26 Mar 2020 19:22:17 +0100 (CET) To: linux-btrfs From: =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= Subject: Q: btrfs and device readahead Organization: Applied Asynchrony, Inc. Message-ID: Date: Thu, 26 Mar 2020 19:22:17 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi, the recent discussion/fixes re. readahead got me thinking: does btrfs use/benefit from a device's readahead setting (/sys/block/sdX/queue/read_ahead_kb) at all or it it completely ignored? Increasing the default from 128k can have drastic effects on other filesystems, but it's not clear (to me) whether this setting is ignored/circumvented by btrfs. I believe (but do not know/understand the details) that this relates to the implemenation of fs->readpages, which AFAIK is about to be replaced by a better/common readahead implementation..correct? Thanks! Holger