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 C46018D0039 for ; Tue, 22 Feb 2011 15:01:49 -0500 (EST) Date: Tue, 22 Feb 2011 13:01:45 -0700 From: Jonathan Corbet Subject: Re: [PATCH 3/5] page_cgroup: make page tracking available for blkio Message-ID: <20110222130145.37cb151e@bike.lwn.net> In-Reply-To: <1298394776-9957-4-git-send-email-arighi@develer.com> References: <1298394776-9957-1-git-send-email-arighi@develer.com> <1298394776-9957-4-git-send-email-arighi@develer.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Righi Cc: Vivek Goyal , Balbir Singh , Daisuke Nishimura , KAMEZAWA Hiroyuki , 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 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. 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. jon -- 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