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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id a1si2936083pgq.38.2019.03.20.19.23.58 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Mar 2019 19:23:58 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b="LJBelv/N"; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org 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=VeDSfNZVcKF/dmMd18yaoimKM6Z0qfa8XNDM5mZkkgM=; b=LJBelv/NWrJP+46sNa0Z0Cxvm Wfe6QsPQy3cLQeSqK18OOxmRL4ocKWa1kpssRKzWLWThOItpi0fQsmjWau7ObsaO14iFhD8LvPVDV 3TNYfRczHJ52/nnWnMukdEvMXIEtu4gnUhE27YHTjnUzWgAbc3g91Np08MiV5f3DdJJg/7auDFG1u ut2WxSoDVNcb5g0jaANLgtFLRISck2fV34uP/kQae4h9lG4sjmEHpKQjLiJHWC3ujqf+9kYzJUvjH 9uz5Uc+Y+3flPehLFAbvQnp4y0pAZQ6VCBal9pnL7jRGOgoLmT5RO/s8XVy+6rJZykRd5DvwXNAE+ SLUxRCAkg==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1h6nN5-0005Us-Vg; Thu, 21 Mar 2019 02:23:55 +0000 Date: Wed, 20 Mar 2019 19:23:55 -0700 From: Matthew Wilcox To: Vlastimil Babka 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 Subject: Re: [RFC 0/2] guarantee natural alignment for kmalloc() Message-ID: <20190321022355.GA19508@bombadil.infradead.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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) 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 Wed, Mar 20, 2019 at 10:48:03PM +0100, Vlastimil Babka wrote: > 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 Hmm. On my laptop, I see: kmalloc-96 28050 35364 96 42 1 : tunables 0 0 0 : slabdata 842 842 0 That'd take me from 842 * 4k pages to 1105 4k pages -- an extra megabyte of memory. This is running Debian's 4.19 kernel: # CONFIG_SLAB is not set CONFIG_SLUB=y # CONFIG_SLOB is not set CONFIG_SLAB_MERGE_DEFAULT=y CONFIG_SLAB_FREELIST_RANDOM=y CONFIG_SLAB_FREELIST_HARDENED=y CONFIG_SLUB_CPU_PARTIAL=y