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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 DB28DC43382 for ; Tue, 25 Sep 2018 00:21:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EED3206B5 for ; Tue, 25 Sep 2018 00:21:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8EED3206B5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728838AbeIYGZ6 (ORCPT ); Tue, 25 Sep 2018 02:25:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55530 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727234AbeIYGZ5 (ORCPT ); Tue, 25 Sep 2018 02:25:57 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5C3CE308A963; Tue, 25 Sep 2018 00:21:11 +0000 (UTC) Received: from ming.t460p (ovpn-8-19.pek2.redhat.com [10.72.8.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B788D8379E; Tue, 25 Sep 2018 00:21:02 +0000 (UTC) Date: Tue, 25 Sep 2018 08:20:58 +0800 From: Ming Lei To: Christopher Lameter Cc: Bart Van Assche , Andrey Ryabinin , Vitaly Kuznetsov , Christoph Hellwig , Ming Lei , linux-block , linux-mm , Linux FS Devel , "open list:XFS FILESYSTEM" , Dave Chinner , Linux Kernel Mailing List , Jens Axboe , Linus Torvalds , Greg Kroah-Hartman Subject: Re: block: DMA alignment of IO buffer allocated from slab Message-ID: <20180925002057.GB14386@ming.t460p> References: <20180920063129.GB12913@lst.de> <87h8ij0zot.fsf@vitty.brq.redhat.com> <20180923224206.GA13618@ming.t460p> <38c03920-0fd0-0a39-2a6e-70cd8cb4ef34@virtuozzo.com> <20a20568-5089-541d-3cee-546e549a0bc8@acm.org> <010001660c27f079-7ba54431-6f0c-430a-8db5-2398a8e761f0-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <010001660c27f079-7ba54431-6f0c-430a-8db5-2398a8e761f0-000000@email.amazonses.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 25 Sep 2018 00:21:11 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 24, 2018 at 03:17:16PM +0000, Christopher Lameter wrote: > On Mon, 24 Sep 2018, Bart Van Assche wrote: > > > /* > > * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned > > * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN > > * aligned pointers. > > */ > > kmalloc alignment is only guaranteed to ARCH_KMALLOC_MINALIGN. That power > of 2 byte caches (without certain options) are aligned to the power of 2 > is due to the nature that these objects are stored in SLUB. Other > allocators may behave different and actually different debug options > result in different alignments. You cannot rely on that. > > ARCH_KMALLOC minalign shows the mininum alignment guarantees. If that is > not sufficient and you do not want to change the arch guarantees then you > can open you own slab cache with kmem_cache_create() where you can specify > different alignment requirements. Christopher, thank you for clarifying the point! Then looks it should be reasonable for XFS to switch to kmem_cache_create() for addressing this issue. Thanks, Ming