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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 AD177C3A59B for ; Fri, 30 Aug 2019 16:55:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8268021897 for ; Fri, 30 Aug 2019 16:55:41 +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="h3Hti2HJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728267AbfH3Qzh (ORCPT ); Fri, 30 Aug 2019 12:55:37 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:55256 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727930AbfH3Qzg (ORCPT ); Fri, 30 Aug 2019 12:55:36 -0400 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=5tlZ2AJFJvBfkQ9+HB/A14V0Nr0ngU+sXRXPgXv+PBY=; b=h3Hti2HJW1XQj8WFYW5QPnxq3 IFR5kBbNPZGUfJLZgkmP05rpU8kdnbpvD+FGCox/WaA3veCbBUk14Fo8QDppOCOnKanexpTcCpiIC sE6OdPzOcn3dr2hQ3CHqWtqGye3D73Fhvq0Q17vVPtbBGqh/n5zn/4vnANjKz08CE7A/cFoQUGoK+ QAYOlb7eXFJYXO9Z2QKijMU6akEztn+q/Y5JPZP/3q07D2/M04Fi6WwQDEhKWs29h7U3KXFx3H23K us6o/usVO3kjrh5OHnBglnCka42lTRpqePeoTQmgPzOXE/Zj/25p3KVTeSiYirbxV1MnU40j6IPKo dF4fbKs+g==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i3kBR-00045V-TF; Fri, 30 Aug 2019 16:55:33 +0000 Date: Fri, 30 Aug 2019 09:55:33 -0700 From: Christoph Hellwig To: Gao Xiang Cc: Christoph Hellwig , linux-fsdevel@vger.kernel.org, devel@driverdev.osuosl.org, Alexander Viro , LKML , Greg Kroah-Hartman , Andrew Morton , Stephen Rothwell , Theodore Ts'o , Pavel Machek , David Sterba , Amir Goldstein , "Darrick J . Wong" , Dave Chinner , Jaegeuk Kim , Jan Kara , Richard Weinberger , Linus Torvalds , linux-erofs@lists.ozlabs.org, Chao Yu , Miao Xie , Li Guifu , Fang Wei Subject: Re: [PATCH v8 20/24] erofs: introduce generic decompression backend Message-ID: <20190830165533.GA10909@infradead.org> References: <20190815044155.88483-1-gaoxiang25@huawei.com> <20190815044155.88483-21-gaoxiang25@huawei.com> <20190830163534.GA29603@infradead.org> <20190830165217.GB107220@architecture4> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190830165217.GB107220@architecture4> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, Aug 31, 2019 at 12:52:17AM +0800, Gao Xiang wrote: > Hi Christoph, > > On Fri, Aug 30, 2019 at 09:35:34AM -0700, Christoph Hellwig wrote: > > On Thu, Aug 15, 2019 at 12:41:51PM +0800, Gao Xiang wrote: > > > +static bool use_vmap; > > > +module_param(use_vmap, bool, 0444); > > > +MODULE_PARM_DESC(use_vmap, "Use vmap() instead of vm_map_ram() (default 0)"); > > > > And how would anyone know which to pick? > > It has significant FIO benchmark difference on sequential read least on arm64... > I have no idea whether all platform vm_map_ram() behaves better than vmap(), > so I leave an option for users here... vm_map_ram is supposed to generally behave better. So if it doesn't please report that that to the arch maintainer and linux-mm so that they can look into the issue. Having user make choices of deep down kernel internals is just a horrible interface. Please talk to maintainers of other bits of the kernel if you see issues and / or need enhancements.