Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755566Ab3IEVZF (ORCPT ); Thu, 5 Sep 2013 17:25:05 -0400 Received: from g5t0009.atlanta.hp.com ([15.192.0.46]:2896 "EHLO g5t0009.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750721Ab3IEVZC (ORCPT ); Thu, 5 Sep 2013 17:25:02 -0400 Message-ID: <5228A1AB.2030308@hp.com> Date: Thu, 05 Sep 2013 15:22:19 +0000 From: Thavatchai Makphaibulchoke User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: Andreas Dilger CC: T Makphaibulchoke , "Theodore Ts'o" , Al Viro , "linux-ext4@vger.kernel.org List" , Linux Kernel Mailing List , "linux-fsdevel@vger.kernel.org Devel" , aswin@hp.com, Linus Torvalds , aswin_proj@groups.hp.com Subject: Re: [PATCH v3 0/2] ext4: increase mbcache scalability References: <1374108934-50550-1-git-send-email-tmac@hp.com> <1378312756-68597-1-git-send-email-tmac@hp.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1620 Lines: 35 On 09/04/2013 08:00 PM, Andreas Dilger wrote: > > In the past, I've raised the question of whether mbcache is even > useful on real-world systems. Essentially, this is providing a > "deduplication" service for ext2/3/4 xattr blocks that are identical. > The question is how often this is actually the case in modern use? > The original design was for allowing external ACL blocks to be > shared between inodes, at a time when ACLs where pretty much the > only xattrs stored on inodes. > > The question now is whether there are common uses where all of the > xattrs stored on multiple inodes are identical? If that is not the > case, mbcache is just adding overhead and should just be disabled > entirely instead of just adding less overhead. > > There aren't good statistics on the hit rate for mbcache, but it > might be possible to generate some with systemtap or similar to > see how often ext4_xattr_cache_find() returns NULL vs. non-NULL. > > Cheers, Andreas > Looks like it's a bit harder to disable mbcache than I thought. I ended up adding code to collect the statics. With selinux enabled, for new_fserver workload of aim7, there are a total of 0x7e05420100000000 ext4_xattr_cache_find() calls that result in a hit and 0xc100000000000000 calls that are not. The number does not seem to favor the complete disabling of mbcache in this case. Thanks, Mak. -- 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/