From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932204AbbAFCZN (ORCPT ); Mon, 5 Jan 2015 21:25:13 -0500 Received: from smtprelay0114.hostedemail.com ([216.40.44.114]:33110 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753697AbbAFCZG (ORCPT ); Mon, 5 Jan 2015 21:25:06 -0500 X-Session-Marker: 6E657665747340676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:965:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:2892:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3874:4390:5007:6261:7875:7901:8660:10004:10400:10848:10967:11026:11232:11658:11914:12043:12296:12517:12519:12740:13069:13095:13148:13230:13255:13311:13357:14096:14097:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: nose59_f2e639bbaa14 X-Filterd-Recvd-Size: 2509 Date: Mon, 5 Jan 2015 21:25:02 -0500 From: Steven Rostedt To: Joonsoo Kim Cc: Hillf Danton , Andrew Morton , "'Christoph Lameter'" , "'Pekka Enberg'" , "'David Rientjes'" , linux-kernel , linux-mm@kvack.org, "'Jesper Dangaard Brouer'" Subject: Re: [PATCH 1/2] mm/slub: optimize alloc/free fastpath by removing preemption on/off Message-ID: <20150105212502.1bdc4f67@gandalf.local.home> In-Reply-To: <20150106013247.GC17222@js1304-P5Q-DELUXE> References: <023701d028c2$dba2cb30$92e86190$@alibaba-inc.com> <20150106013247.GC17222@js1304-P5Q-DELUXE> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 6 Jan 2015 10:32:47 +0900 Joonsoo Kim wrote: > > > +++ b/mm/slub.c > > > @@ -2398,13 +2398,15 @@ redo: > > > * reading from one cpu area. That does not matter as long > > > * as we end up on the original cpu again when doing the cmpxchg. > > > * > > > - * Preemption is disabled for the retrieval of the tid because that > > > - * must occur from the current processor. We cannot allow rescheduling > > > - * on a different processor between the determination of the pointer > > > - * and the retrieval of the tid. > > > + * We should guarantee that tid and kmem_cache are retrieved on > > > + * the same cpu. It could be different if CONFIG_PREEMPT so we need > > > + * to check if it is matched or not. > > > */ > > > - preempt_disable(); > > > - c = this_cpu_ptr(s->cpu_slab); > > > + do { > > > + tid = this_cpu_read(s->cpu_slab->tid); > > > + c = this_cpu_ptr(s->cpu_slab); > > > + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); > > > + barrier(); > > > > Help maintenance more if barrier is documented in commit message. > > Hello, > > Okay. Will add some information about this barrier in commit message. A comment in the commit message is useless. Adding a small comment above the barrier() call itself would be much more useful. -- Steve