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[195.135.220.15]) by mx.google.com with ESMTPS id d14si1246714ede.302.2019.03.20.14.48.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Mar 2019 14:48:07 -0700 (PDT) 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 B61CEAFBD; Wed, 20 Mar 2019 21:48:06 +0000 (UTC) Subject: Re: [RFC 0/2] guarantee natural alignment for kmalloc() To: Matthew Wilcox Cc: Christopher Lameter , linux-mm@kvack.org, Pekka Enberg , David Rientjes , Joonsoo Kim , Ming Lei , Dave Chinner , "Darrick J . Wong" , Christoph Hellwig , Michal Hocko , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org References: <20190319211108.15495-1-vbabka@suse.cz> <01000169988d4e34-b4178f68-c390-472b-b62f-a57a4f459a76-000000@email.amazonses.com> <5d7fee9c-1a80-6ac9-ac1d-b1ce05ed27a8@suse.cz> <20190320185347.GZ19508@bombadil.infradead.org> From: Vlastimil Babka Message-ID: Date: Wed, 20 Mar 2019 22:48:03 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.0 MIME-Version: 1.0 In-Reply-To: <20190320185347.GZ19508@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 3/20/2019 7:53 PM, Matthew Wilcox wrote: > On Wed, Mar 20, 2019 at 09:48:47AM +0100, Vlastimil Babka wrote: >> Natural alignment to size is rather well defined, no? Would anyone ever >> assume a larger one, for what reason? >> It's now where some make assumptions (even unknowingly) for natural >> There are two 'odd' sizes 96 and 192, which will keep cacheline size >> alignment, would anyone really expect more than 64 bytes? > > Presumably 96 will keep being aligned to 32 bytes, as aligning 96 to 64 > just results in 128-byte allocations. Well, looks like that's what happens. This is with SLAB, but the alignment calculations should be common: slabinfo - version: 2.1 # name : tunables : slabdata kmalloc-96 2611 4896 128 32 1 : tunables 120 60 8 : slabdata 153 153 0 kmalloc-128 4798 5536 128 32 1 : tunables 120 60 8 : slabdata 173 173 0