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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 F3E84C10F0B for ; Tue, 26 Feb 2019 10:06:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C141A2173C for ; Tue, 26 Feb 2019 10:06:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727975AbfBZKGS (ORCPT ); Tue, 26 Feb 2019 05:06:18 -0500 Received: from mx2.suse.de ([195.135.220.15]:38402 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727662AbfBZKGR (ORCPT ); Tue, 26 Feb 2019 05:06:17 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F1A58AEA9; Tue, 26 Feb 2019 10:06:14 +0000 (UTC) Subject: Re: [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc To: Ming Lei , Dave Chinner Cc: Matthew Wilcox , "Darrick J . Wong" , linux-xfs@vger.kernel.org, Jens Axboe , Vitaly Kuznetsov , Dave Chinner , Christoph Hellwig , Alexander Duyck , Aaron Lu , Christopher Lameter , Linux FS Devel , linux-mm@kvack.org, linux-block@vger.kernel.org, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim References: <20190225040904.5557-1-ming.lei@redhat.com> <20190225043648.GE23020@dastard> <5ad2ef83-8b3a-0a15-d72e-72652b807aad@suse.cz> <20190225202630.GG23020@dastard> <20190226022249.GA17747@ming.t460p> <20190226030214.GI23020@dastard> <20190226032737.GA11592@bombadil.infradead.org> <20190226045826.GJ23020@dastard> <20190226093302.GA24879@ming.t460p> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 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xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: Date: Tue, 26 Feb 2019 11:06:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190226093302.GA24879@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2/26/19 10:33 AM, Ming Lei wrote: > On Tue, Feb 26, 2019 at 03:58:26PM +1100, Dave Chinner wrote: >> On Mon, Feb 25, 2019 at 07:27:37PM -0800, Matthew Wilcox wrote: >>> On Tue, Feb 26, 2019 at 02:02:14PM +1100, Dave Chinner wrote: >>>>> Or what is the exact size of sub-page IO in xfs most of time? For >>>> >>>> Determined by mkfs parameters. Any power of 2 between 512 bytes and >>>> 64kB needs to be supported. e.g: >>>> >>>> # mkfs.xfs -s size=512 -b size=1k -i size=2k -n size=8k .... >>>> >>>> will have metadata that is sector sized (512 bytes), filesystem >>>> block sized (1k), directory block sized (8k) and inode cluster sized >>>> (32k), and will use all of them in large quantities. >>> >>> If XFS is going to use each of these in large quantities, then it doesn't >>> seem unreasonable for XFS to create a slab for each type of metadata? >> >> >> Well, that is the question, isn't it? How many other filesystems >> will want to make similar "don't use entire pages just for 4k of >> metadata" optimisations as 64k page size machines become more >> common? There are others that have the same "use slab for sector >> aligned IO" which will fall foul of the same problem that has been >> reported for XFS.... >> >> If nobody else cares/wants it, then it can be XFS only. But it's >> only fair we address the "will it be useful to others" question >> first..... > > This kind of slab cache should have been global, just like interface of > kmalloc(size). > > However, the alignment requirement depends on block device's block size, > then it becomes hard to implement as genera interface, for example: > > block size: 512, 1024, 2048, 4096 > slab size: 512*N, 0 < N < PAGE_SIZE/512 > > For 4k page size, 28(7*4) slabs need to be created, and 64k page size > needs to create 127*4 slabs. > Where does the '*4' multiplier come from? So I wonder how hard would it actually be (+CC slab maintainers) to just guarantee generic kmalloc() alignment for power-of-two sizes. If we can do that for kmem_cache_create() then the code should be already there. AFAIK the alignment happens anyway (albeit not guaranteed) in the non-debug cases, and if guaranteeing alignment for certain debugging configurations (that need some space before the object) means larger memory overhead, then the cost should still be bearable since its non-standard configuration where the point is to catch bug and not have peak performance? > But, specific file system may only use some of them, and it depends > on meta data size. > > Thanks, > Ming >