From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by kanga.kvack.org (Postfix) with ESMTP id DC2886B0253 for ; Wed, 4 Nov 2015 09:55:04 -0500 (EST) Received: by padhx2 with SMTP id hx2so47219928pad.1 for ; Wed, 04 Nov 2015 06:55:04 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id ba4si2715258pbb.20.2015.11.04.06.54.51 for ; Wed, 04 Nov 2015 06:54:51 -0800 (PST) Date: Wed, 4 Nov 2015 14:54:46 +0000 From: Catalin Marinas Subject: Re: [PATCH] arm64: Increase the max granular size Message-ID: <20151104145445.GL7637@e104818-lin.cambridge.arm.com> References: <1442944788-17254-1-git-send-email-rric@kernel.org> <20151028190948.GJ8899@e104818-lin.cambridge.arm.com> <20151103120504.GF7637@e104818-lin.cambridge.arm.com> <20151103143858.GI7637@e104818-lin.cambridge.arm.com> <20151103185050.GJ7637@e104818-lin.cambridge.arm.com> <20151104123640.GK7637@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Robert Richter , Joonsoo Kim , Linux-sh list , Will Deacon , "linux-kernel@vger.kernel.org" , Robert Richter , linux-mm@kvack.org, Tirumalesh Chalamarla , Geert Uytterhoeven , "linux-arm-kernel@lists.infradead.org" On Wed, Nov 04, 2015 at 07:53:50AM -0600, Christoph Lameter wrote: > On Wed, 4 Nov 2015, Catalin Marinas wrote: > > > The simplest option would be to make sure that off slab isn't allowed > > for caches of KMALLOC_MIN_SIZE or smaller, with the drawback that not > > only "kmalloc-128" but any other such caches will be on slab. > > The reason for an off slab configuration is denser object packing. > > > I think a better option would be to first check that there is a > > kmalloc_caches[] entry for freelist_size before deciding to go off-slab. > > Hmmm.. Yes seems to be an option. > > Maybe we simply revert commit 8fc9cf420b36 instead? I'm fine with this. Also note that the arm64 commit changing L1_CACHE_BYTES to 128 hasn't been pushed yet (it's queued for 4.4). > That does not seem to make too much sense to me and the goal of the > commit cannot be accomplished on ARM. Your patch essentially reverts > the effect anyways. In theory it only reverts the effect for the first kmalloc_cache ("kmalloc-128" in the arm64 case). Any other bigger cache which would not be mergeable with an existing one still has the potential of off-slab management. > Smaller slabs really do not need off slab management anyways since they > will only loose a few objects per slab page. IIUC, starting with 128 slab size for a 4KB page, you have 32 objects per page. The freelist takes 32 bytes (or 31), therefore you waste a single slab object. However, only 1/4 of it is used for freelist and the waste gets bigger with 256 slab size, hence the original commit. BTW, assuming L1_CACHE_BYTES is 512 (I don't ever see this happening but just in theory), we potentially have the same issue. What would save us is that INDEX_NODE would match the first "kmalloc-512" cache, so we have it pre-populated. -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org