From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d28relay04.in.ibm.com (d28relay04.in.ibm.com [9.184.220.61]) by e28esmtp02.in.ibm.com (8.13.1/8.13.1) with ESMTP id m813SWic000526 for ; Mon, 1 Sep 2008 08:58:32 +0530 Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay04.in.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m813SVwj1794262 for ; Mon, 1 Sep 2008 08:58:31 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.13.1/8.13.3) with ESMTP id m813SVVd032702 for ; Mon, 1 Sep 2008 08:58:31 +0530 Message-ID: <48BB6160.4070904@linux.vnet.ibm.com> Date: Mon, 01 Sep 2008 08:58:32 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com MIME-Version: 1.0 Subject: Re: [RFC][PATCH] Remove cgroup member from struct page References: <20080831174756.GA25790@balbir.in.ibm.com> <20080901090102.46b75141.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20080901090102.46b75141.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: Andrew Morton , hugh@veritas.com, menage@google.com, xemul@openvz.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "nickpiggin@yahoo.com.au" List-ID: KAMEZAWA Hiroyuki wrote: > On Sun, 31 Aug 2008 23:17:56 +0530 > Balbir Singh wrote: > >> This is a rewrite of a patch I had written long back to remove struct page >> (I shared the patches with Kamezawa, but never posted them anywhere else). >> I spent the weekend, cleaning them up for 2.6.27-rc5-mmotm (29 Aug 2008). >> > It's just because I think there is no strong requirements for 64bit count/mapcount. > There is no ZERO_PAGE() for ANON (by Nick Piggin. I add him to CC.) > (shmem still use it but impact is not big.) > I understand the comment, but not it's context. Are you suggesting that the sizeof _count and _mapcount can be reduced? Hence the impact of having a member in struct page is not all that large? I think the patch is definitely very important for 32 bit systems. >> I've tested the patches on an x86_64 box, I've run a simple test running >> under the memory control group and the same test running concurrently under >> two different groups (and creating pressure within their groups). I've also >> compiled the patch with CGROUP_MEM_RES_CTLR turned off. >> >> Advantages of the patch >> >> 1. It removes the extra pointer in struct page >> >> Disadvantages >> >> 1. It adds an additional lock structure to struct page_cgroup >> 2. Radix tree lookup is not an O(1) operation, once the page is known >> getting to the page_cgroup (pc) is a little more expensive now. >> >> This is an initial RFC for comments >> >> TODOs >> >> 1. Test the page migration changes >> 2. Test the performance impact of the patch/approach >> >> Comments/Reviews? >> > plz wait until lockless page cgroup.... > That depends, if we can get the lockless page cgroup done quickly, I don't mind waiting, but if it is going to take longer, I would rather push these changes in. There should not be too much overhead in porting lockless page cgroup patch on top of this (remove pc->lock and use pc->flags). I'll help out, so as to avoid wastage of your effort. > And If you don't support radix-tree-delete(), pre-allocating all at boot is better. > We do use radix-tree-delete() in the code, please see below. Pre-allocating has the disadvantage that we will pre-allocate even for kernel pages, etc. > BTW, why pc->lock is necessary ? It increases size of struct page_cgroup and reduce > the advantege of your patch's to half (8bytes -> 4bytes). > Yes, I've mentioned that as a disadvantage. Are you suggesting that with lockless page cgroup we won't need pc->lock? > Thanks, > -Kame -- Balbir -- 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