From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753335Ab1HZPCq (ORCPT ); Fri, 26 Aug 2011 11:02:46 -0400 Received: from mail-pz0-f42.google.com ([209.85.210.42]:62160 "EHLO mail-pz0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774Ab1HZPCq (ORCPT ); Fri, 26 Aug 2011 11:02:46 -0400 Subject: Re: [PATCH] slab: avoid unnecessary touching of a partial slab From: Zhao Jin To: Christoph Lameter Cc: penberg@kernel.org, mpm@selenic.com, trivial@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: References: <1314370016.8991.38.camel@vm> Content-Type: text/plain; charset="us-ascii" Date: Fri, 26 Aug 2011 23:02:34 +0800 Message-ID: <1314370954.8991.46.camel@vm> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2011-08-26 at 09:50 -0500, Christoph Lameter wrote: > On Fri, 26 Aug 2011, Zhao Jin wrote: > > > On Fri, 2011-08-26 at 09:08 -0500, Christoph Lameter wrote: > > > On Fri, 26 Aug 2011, Zhao Jin wrote: > > > > > > > In cache_alloc_refill(), after refilling from a partial slab, if the > > > > slab remains partial, it would be deleted from and then added again to > > > > the partial list. As the slab is the first element in the list before > > > > deletion, such behavior has no effect. This patch avoids touching the > > > > slab in this case. > > > > > > The list_del/list_add action is a list_move. > > > > But in cache_alloc_refill(), it is the first slab (that is: its list > > field is pointed by the l3->slabs_partial.next) that is picked from the > > partial list for refilling. Assume it remains partial after that. Since > > list_add inserts a new element after the head (l3->slabs_partial), the > > position of the slab in the partial list won't change after > > list_del/list_add: it will be still the first element. Therefore, > > list_del/list_add has done nothing actually in this case. > > Correct but still tthe del/add is a list_move operation. Convert that the > other case as well? > Yes. The patch avoids list_del/list_add only if it is the case that a partial slab was used for refilling and remains partial (that is: partial => partial). If it is not the case( so it must be either partial => full, free => full or free => partial) the patched code behaves the same as current (list_del/list_add). Regards, zhj