From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx142.postini.com [74.125.245.142]) by kanga.kvack.org (Postfix) with SMTP id 3B62E6B0005 for ; Wed, 6 Mar 2013 01:58:46 -0500 (EST) Received: by mail-pb0-f50.google.com with SMTP id up1so5590125pbc.37 for ; Tue, 05 Mar 2013 22:58:45 -0800 (PST) Message-ID: <5136E91C.3020700@gmail.com> Date: Wed, 06 Mar 2013 14:58:36 +0800 From: Ric Mason MIME-Version: 1.0 Subject: Re: [PATCH 2/7] ksm: treat unstable nid like in stable tree References: <51271A7D.6020305@gmail.com> <51303CAB.3080406@gmail.com> <51315174.4020200@gmail.com> <5136ABEE.8000501@gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Andrew Morton , Mel Gorman , Petr Holasek , Andrea Arcangeli , Izik Eidus , linux-kernel@vger.kernel.org, linux-mm@kvack.org Hi Hugh, On 03/06/2013 01:05 PM, Hugh Dickins wrote: > On Wed, 6 Mar 2013, Ric Mason wrote: > [ I've deleted the context because that was about the unstable tree, > and here you have moved to asking about a case in the stable tree. ] >> For the case of a ksm page is migrated to a different NUMA node and migrate >> its stable node to the right tree and collide with an existing stable node. >> get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid) can capture nothing > That's not so: as I've pointed out before, ksm_migrate_page() updates > stable_node->kpfn for the new page on the new NUMA node; but it cannot > (get the right locking to) move the stable_node to its new tree at that time. > > It's moved out once ksmd notices that it's in the wrong NUMA node tree - > perhaps when one its rmap_items reaches the head of cmp_and_merge_page(), > or perhaps here in stable_tree_search() when it matches another page > coming in to cmp_and_merge_page(). > > You may be concentrating on the case when that "another page" is a ksm > page migrated from a different NUMA node; and overlooking the case of > when the matching ksm page in this stable tree has itself been migrated. > >> since stable_node is the node in the right stable tree, nothing happen to it >> before this check. Did you intend to check get_kpfn_nid(page_node->kpfn) != >> NUMA(page_node->nid) ? > Certainly not: page_node is usually NULL. But I could have checked Are you sure? list_del(&page_node->list) and DO_NUMA(page_node->nid = nid) will trigger panic now. > get_kpfn_nid(stable_node->kpfn) != nid: I was duplicating the test > from cmp_and_merge_page(), but here we do have local variable nid. > > Hugh -- 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