Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752284Ab0HBXt5 (ORCPT ); Mon, 2 Aug 2010 19:49:57 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:36603 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750836Ab0HBXt4 (ORCPT ); Mon, 2 Aug 2010 19:49:56 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 3 Aug 2010 08:45:00 +0900 From: KAMEZAWA Hiroyuki To: balbir@linux.vnet.ibm.com Cc: Andrew Morton , "linux-mm@kvack.org" , "nishimura@mxp.nes.nec.co.jp" , gthelen@google.com, m-ikeda@ds.jp.nec.com, "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH 1/7][memcg] virtually indexed array library. Message-Id: <20100803084500.8bf99ff2.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100802180051.GX3863@balbir.in.ibm.com> References: <20100727165155.8b458b7f.kamezawa.hiroyu@jp.fujitsu.com> <20100727165303.7d7d18e9.kamezawa.hiroyu@jp.fujitsu.com> <20100728124513.85bfa047.akpm@linux-foundation.org> <20100729093226.7b899930.kamezawa.hiroyu@jp.fujitsu.com> <20100729132703.2d53e8a4.kamezawa.hiroyu@jp.fujitsu.com> <20100802180051.GX3863@balbir.in.ibm.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) 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 Content-Length: 1673 Lines: 45 On Mon, 2 Aug 2010 23:30:51 +0530 Balbir Singh wrote: > * KAMEZAWA Hiroyuki [2010-07-29 13:27:03]: > > > On Thu, 29 Jul 2010 09:32:26 +0900 > > KAMEZAWA Hiroyuki wrote: > > > > > On Wed, 28 Jul 2010 12:45:13 -0700 > > > Andrew Morton wrote: > > > > > > My gut reaction to this sort of thing is "run away in terror". It > > > > encourages kernel developers to operate like lackadaisical userspace > > > > developers and to assume that underlying code can perform heroic and > > > > immortal feats. But it can't. This is the kernel and the kernel is a > > > > tough and hostile place and callers should be careful and defensive and > > > > take great efforts to minimise the strain they put upon other systems. > > > > > > > > IOW, can we avoid doing this? > > > > > > > > > > > I'll use pre-allocated pointer array in the next version. It's simple even > > if a bit slow. > > > > == > > struct mem_cgroup *mem_cgroups[CONFIG_MAX_MEM_CGROUPS] __read_mostly; > > #define id_to_memcg(id) mem_cgroups[id]; > > == > > Hmm.. I thought we were going to reuse css_id() and use that to get to > the cgroup. May be I am missing something. > ? lookup_css_id() requires multi-level table lookup because of radix-tree. And compiler can't generate an optimized code. linear table lookup is quick. -Kame -- 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/