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[195.135.220.15]) by mx.google.com with ESMTPS id l2si5054016ejs.241.2019.02.26.23.10.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Feb 2019 23:10:43 -0800 (PST) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz 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 C8F49B02D; Wed, 27 Feb 2019 07:10:42 +0000 (UTC) Subject: Re: [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc To: Matthew Wilcox , "Darrick J. Wong" Cc: Ming Lei , Ming Lei , Dave Chinner , "open list:XFS FILESYSTEM" , Jens Axboe , Vitaly Kuznetsov , Dave Chinner , Christoph Hellwig , Alexander Duyck , Aaron Lu , Christopher Lameter , Linux FS Devel , linux-mm , linux-block , Pekka Enberg , David Rientjes , Joonsoo Kim References: <20190226045826.GJ23020@dastard> <20190226093302.GA24879@ming.t460p> <20190226121209.GC11592@bombadil.infradead.org> <20190226123545.GA6163@ming.t460p> <20190226130230.GD11592@bombadil.infradead.org> <20190226134247.GA30942@ming.t460p> <20190226140440.GF11592@bombadil.infradead.org> <20190226161433.GH21626@magnolia> <20190226161912.GG11592@bombadil.infradead.org> 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: <095ae112-f98e-9516-910a-43b49ea5bf0d@suse.cz> Date: Wed, 27 Feb 2019 08:07:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190226161912.GG11592@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2/26/19 5:19 PM, Matthew Wilcox wrote: > On Tue, Feb 26, 2019 at 08:14:33AM -0800, Darrick J. Wong wrote: >> On Tue, Feb 26, 2019 at 06:04:40AM -0800, Matthew Wilcox wrote: >> Wait a minute, are you all saying that /directio/ is broken on XFS too?? >> XFS doesn't use blockdev_direct_IO anymore. >> >> I thought we were talking about alignment of XFS metadata buffers >> (xfs_buf.c), which is a very different topic. >> >> As I understand the problem, in non-debug mode the slab caches give >> xfs_buf chunks of memory that are aligned well enough to work, but in >> debug mode the slabs allocate slightly more bytes to carry debug >> information which pushes the returned address up slightly, thus breaking >> the alignment requirements. >> >> So why can't we just move the debug info to the end of the object? If >> our 512 byte allocation turns into a (512 + a few more) bytes we'll end >> up using 1024 bytes on the allocation regardless, so it shouldn't matter >> to put the debug info at offset 512. If the reason is fear that kernel >> code will scribble off the end of the object, then return (*obj + 512). >> Maybe you all have already covered this, though? > > I don't know _what_ Ming Lei is saying. I thought the problem was > with slab redzones, which need to be before and after each object, > but apparently the problem is with KASAN as well. That's what I thought as well. But if we can solve it for caches created by kmem_cache_create(..., align, ...) then IMHO we could guarantee natural alignment for power-of-two kmalloc caches as well.