From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 6CCBB8D0039 for ; Tue, 22 Feb 2011 23:56:06 -0500 (EST) Received: from m4.gw.fujitsu.co.jp (unknown [10.0.50.74]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id F0DB43EE0C2 for ; Wed, 23 Feb 2011 13:56:01 +0900 (JST) Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id D13A945DE57 for ; Wed, 23 Feb 2011 13:56:01 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id B7B1F45DE52 for ; Wed, 23 Feb 2011 13:56:01 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id A26761DB8042 for ; Wed, 23 Feb 2011 13:56:01 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 640561DB8037 for ; Wed, 23 Feb 2011 13:56:01 +0900 (JST) Date: Wed, 23 Feb 2011 13:49:10 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 3/5] page_cgroup: make page tracking available for blkio Message-Id: <20110223134910.abbdc931.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110222233718.GF23723@linux.develer.com> References: <1298394776-9957-1-git-send-email-arighi@develer.com> <1298394776-9957-4-git-send-email-arighi@develer.com> <20110222130145.37cb151e@bike.lwn.net> <20110222230146.GB23723@linux.develer.com> <20110222230630.GL28269@redhat.com> <20110222233718.GF23723@linux.develer.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Righi Cc: Vivek Goyal , Jonathan Corbet , Balbir Singh , Daisuke Nishimura , Greg Thelen , Wu Fengguang , Gui Jianfeng , Ryo Tsuruta , Hirokazu Takahashi , Jens Axboe , Andrew Morton , containers@lists.linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 23 Feb 2011 00:37:18 +0100 Andrea Righi wrote: > On Tue, Feb 22, 2011 at 06:06:30PM -0500, Vivek Goyal wrote: > > On Wed, Feb 23, 2011 at 12:01:47AM +0100, Andrea Righi wrote: > > > On Tue, Feb 22, 2011 at 01:01:45PM -0700, Jonathan Corbet wrote: > > > > On Tue, 22 Feb 2011 18:12:54 +0100 > > > > Andrea Righi wrote: > > > > > > > > > The page_cgroup infrastructure, currently available only for the memory > > > > > cgroup controller, can be used to store the owner of each page and > > > > > opportunely track the writeback IO. This information is encoded in > > > > > the upper 16-bits of the page_cgroup->flags. > > > > > > > > > > A owner can be identified using a generic ID number and the following > > > > > interfaces are provided to store a retrieve this information: > > > > > > > > > > unsigned long page_cgroup_get_owner(struct page *page); > > > > > int page_cgroup_set_owner(struct page *page, unsigned long id); > > > > > int page_cgroup_copy_owner(struct page *npage, struct page *opage); > > > > > > > > My immediate observation is that you're not really tracking the "owner" > > > > here - you're tracking an opaque 16-bit token known only to the block > > > > controller in a field which - if changed by anybody other than the block > > > > controller - will lead to mayhem in the block controller. I think it > > > > might be clearer - and safer - to say "blkcg" or some such instead of > > > > "owner" here. > > > > > > > > > > Basically the idea here was to be as generic as possible and make this > > > feature potentially available also to other subsystems, so that cgroup > > > subsystems may represent whatever they want with the 16-bit token. > > > However, no more than a single subsystem may be able to use this feature > > > at the same time. > > > > > > > I'm tempted to say it might be better to just add a pointer to your > > > > throtl_grp structure into struct page_cgroup. Or maybe replace the > > > > mem_cgroup pointer with a single pointer to struct css_set. Both of > > > > those ideas, though, probably just add unwanted extra overhead now to gain > > > > generality which may or may not be wanted in the future. > > > > > > The pointer to css_set sounds good, but it would add additional space to > > > the page_cgroup struct. Now, page_cgroup is 40 bytes (in 64-bit arch) > > > and all of them are allocated at boot time. Using unused bits in > > > page_cgroup->flags is a choice with no overhead from this point of view. > > > > I think John suggested replacing mem_cgroup pointer with css_set so that > > size of the strcuture does not increase but it leads extra level of > > indirection. > > OK, got it sorry. > > So, IIUC we save css_set pointer and get a struct cgroup as following: > > struct cgroup *cgrp = css_set->subsys[subsys_id]->cgroup; > > Then, for example to get the mem_cgroup reference: > > struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp); > > It seems a lot of indirections, but I may have done something wrong or > there could be a simpler way to do it. > Then, page_cgroup should have reference count on css_set and make tons of atomic ops. BTW, bits of pc->flags are used for storing sectionID or nodeID. Please clarify your 16bit never breaks that information. And please keep more 4-5 flags for dirty_ratio support of memcg. I wonder I can make pc->mem_cgroup to be pc->memid(16bit), then, == static inline struct mem_cgroup *get_memcg_from_pc(struct page_cgroup *pc) { struct cgroup_subsys_state *css = css_lookup(&mem_cgroup_subsys, pc->memid); return container_of(css, struct mem_cgroup, css); } == Overhead will be seen at updating file statistics and LRU management. But, hmm, can't you do that tracking without page_cgroup ? Because the number of dirty/writeback pages are far smaller than total pages, chasing I/O with dynamic structure is not very bad.. prepareing [pfn -> blkio] record table and move that information to struct bio in dynamic way is very difficult ? 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org