From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx152.postini.com [74.125.245.152]) by kanga.kvack.org (Postfix) with SMTP id 2EA7C6B004A for ; Tue, 21 Feb 2012 15:13:23 -0500 (EST) Received: by dadv6 with SMTP id v6so8888118dad.14 for ; Tue, 21 Feb 2012 12:13:22 -0800 (PST) Date: Tue, 21 Feb 2012 12:12:58 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 9/10] mm/memcg: move lru_lock into lruvec In-Reply-To: <4F434300.3080001@openvz.org> Message-ID: References: <4F434300.3080001@openvz.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov Cc: Andrew Morton , KAMEZAWA Hiroyuki , Johannes Weiner , Ying Han , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" On Tue, 21 Feb 2012, Konstantin Khlebnikov wrote: > > On lumpy/compaction isolate you do: > > if (!PageLRU(page)) > continue > > __isolate_lru_page() > > page_relock_rcu_vec() > rcu_read_lock() > rcu_dereference()... > spin_lock()... > rcu_read_unlock() > > You protect page_relock_rcu_vec with switching pointers back to root. > > I do: > > catch_page_lru() > rcu_read_lock() > if (!PageLRU(page)) > return false > rcu_dereference()... > spin_lock()... > rcu_read_unlock() > if (PageLRU()) > return true > if true > __isolate_lru_page() > > I protect my catch_page_lruvec() with PageLRU() under single rcu-interval > with locking. > Thus my code is better, because it not requires switching pointers back to > root memcg. That sounds much better, yes - if it does work reliably. I'll have to come back to think about your locking later too; or maybe that's exactly where I need to look, when investigating the mm_inline.h:41 BUG. But at first sight, I have to say I'm very suspicious: I've never found PageLRU a good enough test for whether we need such a lock, because of races with those pages on percpu lruvec about to be put on the lru. But maybe once I look closer, I'll find that's handled by your changes away from lruvec; though I'd have thought the same issue exists, independent of whether the pending pages are in vector or list. Hugh > > Meanwhile after seeing your patches, I realized that this rcu-protection is > required only for lock-by-pfn in lumpy/compaction isolation. > Thus my locking should be simplified and optimized. -- 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