From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753991AbaEOPPP (ORCPT ); Thu, 15 May 2014 11:15:15 -0400 Received: from qmta05.emeryville.ca.mail.comcast.net ([76.96.30.48]:58777 "EHLO qmta05.emeryville.ca.mail.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751174AbaEOPPO (ORCPT ); Thu, 15 May 2014 11:15:14 -0400 Date: Thu, 15 May 2014 10:15:10 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Vladimir Davydov cc: hannes@cmpxchg.org, mhocko@suse.cz, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC 1/3] slub: keep full slabs on list for per memcg caches In-Reply-To: <20140515063441.GA32113@esperanza> Message-ID: References: <20140515063441.GA32113@esperanza> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 15 May 2014, Vladimir Davydov wrote: > > That will significantly impact the fastpaths for alloc and free. > > > > Also a pretty significant change the logic of the fastpaths since they > > were not designed to handle the full lists. In debug mode all operations > > were only performed by the slow paths and only the slow paths so far > > supported tracking full slabs. > > That's the minimal price we have to pay for slab re-parenting, because > w/o it we won't be able to look up for all slabs of a particular per > memcg cache. The question is, can it be tolerated or I'd better try some > other way? AFACIT these modifications all together will have a significant impact on performance. You could avoid the refcounting on free relying on the atomic nature of cmpxchg operations. If you zap the per cpu slab then the fast path will be forced to fall back to the slowpaths where you could do what you need to do. There is no tracking of full slabs without adding much more logic to the fastpath. You could force any operation that affects tne full list into the slow path. But that also would have an impact.