From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Lameter Subject: Re: [patch 21/21] slab defrag: Obsolete SLAB Date: Wed, 14 May 2008 15:32:17 -0700 (PDT) Message-ID: References: <482B2617.5010605@firstfloor.org> <20080514205842.GC9921@parisc-linux.org> <20080514212130.GD9921@parisc-linux.org> <20080514214326.GF9921@parisc-linux.org> <20080514220058.GG9921@parisc-linux.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Andi Kleen , Pekka Enberg , KOSAKI Motohiro , Rik van Riel , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Mel Gorman , mpm@selenic.com, "Zhang, Yanmin" To: Matthew Wilcox Return-path: Received: from relay1.sgi.com ([192.48.171.29]:48775 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753763AbYENWcV (ORCPT ); Wed, 14 May 2008 18:32:21 -0400 In-Reply-To: <20080514220058.GG9921@parisc-linux.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 14 May 2008, Matthew Wilcox wrote: > Since there's no way we've found to date to get the TPC test to you, > how about we settle for analysing _this_ testcase which did show a > significant performance degradation for slub? > > I don't think it's an unreasonable testcase either -- effectively it's > allocating memory on all CPUs and then freeing it all on one. If that's > a worst-case scenario for slub, then slub isn't suitable for replacing > slab yet. Indeed that is a worst case scenario due to finer grained locking. The opposite side of that is that fast concurrent freeing of objects from two processors will have higher performance in slub since there is significantly less global lock contention and less work with expiring objects and moving them around (if you hit the queue limits then SLAB will do synchroonous merging of objects into slabs, its then no longer able to hide the object handling overhead in cache_reap().)