From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 524F2600429 for ; Mon, 2 Aug 2010 19:46:53 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o72Nnp1A009004 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 3 Aug 2010 08:49:51 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 444B545DE4F for ; Tue, 3 Aug 2010 08:49:51 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 2150445DE4E for ; Tue, 3 Aug 2010 08:49:51 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id E41A51DB804F for ; Tue, 3 Aug 2010 08:49:50 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id 9DD611DB8044 for ; Tue, 3 Aug 2010 08:49:50 +0900 (JST) Date: Tue, 3 Aug 2010 08:45:00 +0900 From: KAMEZAWA Hiroyuki 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org 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" List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org