From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755255Ab3AZB7g (ORCPT ); Fri, 25 Jan 2013 20:59:36 -0500 Received: from mail-pa0-f53.google.com ([209.85.220.53]:60529 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753468Ab3AZB7e (ORCPT ); Fri, 25 Jan 2013 20:59:34 -0500 Date: Fri, 25 Jan 2013 17:59:35 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Petr Holasek , Andrea Arcangeli , Izik Eidus , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 4/11] ksm: reorganize ksm_check_stable_tree In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Memory hotremove's ksm_check_stable_tree() is pitifully inefficient (restarting whenever it finds a stale node to remove), but rearrange so that at least it does not needlessly restart from nid 0 each time. And add a couple of comments: here is why we keep pfn instead of page. Signed-off-by: Hugh Dickins --- mm/ksm.c | 38 ++++++++++++++++++++++---------------- 1 file changed, 22 insertions(+), 16 deletions(-) --- mmotm.orig/mm/ksm.c 2013-01-25 14:36:52.152205940 -0800 +++ mmotm/mm/ksm.c 2013-01-25 14:36:53.244205966 -0800 @@ -1830,31 +1830,36 @@ void ksm_migrate_page(struct page *newpa #endif /* CONFIG_MIGRATION */ #ifdef CONFIG_MEMORY_HOTREMOVE -static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn, - unsigned long end_pfn) +static void ksm_check_stable_tree(unsigned long start_pfn, + unsigned long end_pfn) { + struct stable_node *stable_node; struct rb_node *node; int nid; - for (nid = 0; nid < nr_node_ids; nid++) - for (node = rb_first(&root_stable_tree[nid]); node; - node = rb_next(node)) { - struct stable_node *stable_node; - + for (nid = 0; nid < nr_node_ids; nid++) { + node = rb_first(&root_stable_tree[nid]); + while (node) { stable_node = rb_entry(node, struct stable_node, node); if (stable_node->kpfn >= start_pfn && - stable_node->kpfn < end_pfn) - return stable_node; + stable_node->kpfn < end_pfn) { + /* + * Don't get_ksm_page, page has already gone: + * which is why we keep kpfn instead of page* + */ + remove_node_from_stable_tree(stable_node); + node = rb_first(&root_stable_tree[nid]); + } else + node = rb_next(node); + cond_resched(); } - - return NULL; + } } static int ksm_memory_callback(struct notifier_block *self, unsigned long action, void *arg) { struct memory_notify *mn = arg; - struct stable_node *stable_node; switch (action) { case MEM_GOING_OFFLINE: @@ -1874,11 +1879,12 @@ static int ksm_memory_callback(struct no /* * Most of the work is done by page migration; but there might * be a few stable_nodes left over, still pointing to struct - * pages which have been offlined: prune those from the tree. + * pages which have been offlined: prune those from the tree, + * otherwise get_ksm_page() might later try to access a + * non-existent struct page. */ - while ((stable_node = ksm_check_stable_tree(mn->start_pfn, - mn->start_pfn + mn->nr_pages)) != NULL) - remove_node_from_stable_tree(stable_node); + ksm_check_stable_tree(mn->start_pfn, + mn->start_pfn + mn->nr_pages); /* fallthrough */ case MEM_CANCEL_OFFLINE: