Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754057Ab3IJFn1 (ORCPT ); Tue, 10 Sep 2013 01:43:27 -0400 Received: from lgeamrelo01.lge.com ([156.147.1.125]:45695 "EHLO LGEAMRELO01.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752533Ab3IJFn0 (ORCPT ); Tue, 10 Sep 2013 01:43:26 -0400 X-AuditID: 9c93017d-b7cdfae0000026c0-ef-522eb17b2123 Date: Tue, 10 Sep 2013 14:43:42 +0900 From: Joonsoo Kim To: Christoph Lameter Cc: Pekka Enberg , Andrew Morton , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [REPOST PATCH 3/4] slab: introduce byte sized index for the freelist of a slab Message-ID: <20130910054342.GB24602@lge.com> References: <1378447067-19832-1-git-send-email-iamjoonsoo.kim@lge.com> <1378447067-19832-4-git-send-email-iamjoonsoo.kim@lge.com> <00000140f3fed229-f49b95d4-7087-476f-b2c9-37846749aad6-000000@email.amazonses.com> <20130909043217.GB22390@lge.com> <00000141032dea11-c5aa9c77-b2f2-4cab-b7a0-d37665a6cec8-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00000141032dea11-c5aa9c77-b2f2-4cab-b7a0-d37665a6cec8-000000@email.amazonses.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2563 Lines: 50 On Mon, Sep 09, 2013 at 02:44:03PM +0000, Christoph Lameter wrote: > On Mon, 9 Sep 2013, Joonsoo Kim wrote: > > > 32 byte is not minimum object size, minimum *kmalloc* object size > > in default configuration. There are some slabs that their object size is > > less than 32 byte. If we have a 8 byte sized kmem_cache, it has 512 objects > > in 4K page. > > As far as I can recall only SLUB supports 8 byte objects. SLABs mininum > has always been 32 bytes. No. There are many slabs that their object size are less than 32 byte. And I can also create a 8 byte sized slab in my kernel with SLAB. js1304@js1304-P5Q-DELUXE:~/Projects/remote_git/linux$ sudo cat /proc/slabinfo | awk '{if($4 < 32) print $0}' slabinfo - version: 2.1 ecryptfs_file_cache 0 0 16 240 1 : tunables 120 60 8 : slabdata 0 0 0 jbd2_revoke_table_s 2 240 16 240 1 : tunables 120 60 8 : slabdata 1 1 0 journal_handle 0 0 24 163 1 : tunables 120 60 8 : slabdata 0 0 0 revoke_table 0 0 16 240 1 : tunables 120 60 8 : slabdata 0 0 0 scsi_data_buffer 0 0 24 163 1 : tunables 120 60 8 : slabdata 0 0 0 fsnotify_event_holder 0 0 24 163 1 : tunables 120 60 8 : slabdata 0 0 0 numa_policy 3 163 24 163 1 : tunables 120 60 8 : slabdata 1 1 0 > > > Moreover, we can configure slab_max_order in boot time so that we can't know > > how many object are in a certain slab in compile time. Therefore we can't > > decide the size of the index in compile time. > > You can ignore the slab_max_order if necessary. > > > I think that byte and short int sized index support would be enough, but > > it should be determined at runtime. > > On x86 f.e. it would add useless branching. The branches are never taken. > You only need these if you do bad things to the system like requiring > large contiguous allocs. As I said before, since there is a possibility that some runtime loaded modules use a 8 byte sized slab, we can't determine index size in compile time. Otherwise we should always use short int sized index and I think that it is worse than adding a branch. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/