From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 1 Sep 2008 13:03:51 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH] Remove cgroup member from struct page Message-Id: <20080901130351.f005d5b6.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <48BB6160.4070904@linux.vnet.ibm.com> References: <20080831174756.GA25790@balbir.in.ibm.com> <20080901090102.46b75141.kamezawa.hiroyu@jp.fujitsu.com> <48BB6160.4070904@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: balbir@linux.vnet.ibm.com 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: On Mon, 01 Sep 2008 08:58:32 +0530 Balbir Singh wrote: > 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. Maybe they cannot be reduced. For 32bit systems, if the machine doesn't equip crazy amounts of memory (as 32GB) I don't think this 32bit is not very large. Let's calculate. 1GB/4096 x 4 bytes = 1 MB per 1GB. But you adds spinlock_t, then what this patch reduce is not so big. Maybe only hundreds of kilobytes. (All pages in HIGHMEM will be used with structpage_cgroup.) > >> 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. The development of lockless-page_cgroup is not stalled. I'm just waiting for my 8cpu box comes back from maintainance... If you want to see, I'll post v3 with brief result on small (2cpu) box. > 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. > Sorry. I missed pc==NULL case. > > 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? > Not so clear at this stage. Thanks, -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