From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 22AA16B004D for ; Tue, 20 Dec 2011 22:25:19 -0500 (EST) Received: by iacb35 with SMTP id b35so12246490iac.14 for ; Tue, 20 Dec 2011 19:25:18 -0800 (PST) Date: Tue, 20 Dec 2011 19:25:04 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH] memcg: reset to root_mem_cgroup at bypassing In-Reply-To: <20111221091347.4f1a10d8.kamezawa.hiroyu@jp.fujitsu.com> Message-ID: References: <20111219165146.4d72f1bb.kamezawa.hiroyu@jp.fujitsu.com> <20111221091347.4f1a10d8.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="8323584-472047041-1324437918=:1310" Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Hiroyuki Kamezawa , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , cgroups@vger.kernel.org, "linux-kernel@vger.kernel.org" , "hannes@cmpxchg.org" , Michal Hocko This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323584-472047041-1324437918=:1310 Content-Type: TEXT/PLAIN; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Wed, 21 Dec 2011, KAMEZAWA Hiroyuki wrote: > On Tue, 20 Dec 2011 09:24:47 +0900 > Hiroyuki Kamezawa wrote: > > 2011/12/20 Hugh Dickins : > >=20 > > > I speak from experience: I did *exactly* the same at "bypass" when > > > I introduced our mem_cgroup_reset_page(), which corresponds to your > > > mem_cgroup_reset_owner(); it seemed right to me that a successful > > > (return 0) call to try_charge() should provide a good *ptr. > > > > > ok. > >=20 > > > But others (Ying and Greg) pointed out that it changes the semantics > > > of __mem_cgroup_try_charge() in this case, so you need to justify the > > > change to all those places which do something like "if (ret || !memcg= )" > > > after calling it. =C2=A0Perhaps it is a good change everywhere, but t= hat's > > > not obvious, so we chose caution. > > > > > > Doesn't it lead to bypass pages being marked as charged to root, so > > > they don't get charged to the right owner next time they're touched? > > > > > Yes. You're right. > > Hm. So, it seems I should add reset_owner() to the !memcg path > > rather than here. > >=20 > Considering this again.. >=20 > Now, we catch 'charge' event only once in lifetime of anon/file page. > So, it doesn't depend on that it's marked as PCG_USED or not. That's an interesting argument, I hadn't been looking at it that way. It's not true of swapcache, but I guess we don't need to preserve its peculiarities in this case. I've not checked the (ret || !memcg) cases yet to see if any change needed there. I certainly like that the success return guarantees that memcg is set. Hugh --8323584-472047041-1324437918=:1310-- -- 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