Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755480Ab0DTVDv (ORCPT ); Tue, 20 Apr 2010 17:03:51 -0400 Received: from gir.skynet.ie ([193.1.99.77]:47018 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755301Ab0DTVBN (ORCPT ); Tue, 20 Apr 2010 17:01:13 -0400 From: Mel Gorman To: Andrew Morton Cc: Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , Minchan Kim , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Rik van Riel , Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages Date: Tue, 20 Apr 2010 22:01:06 +0100 Message-Id: <1271797276-31358-5-git-send-email-mel@csn.ul.ie> X-Mailer: git-send-email 1.6.5 In-Reply-To: <1271797276-31358-1-git-send-email-mel@csn.ul.ie> References: <1271797276-31358-1-git-send-email-mel@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3769 Lines: 116 PageAnon pages that are unmapped may or may not have an anon_vma so are not currently migrated. However, a swap cache page can be migrated and fits this description. This patch identifies page swap caches and allows them to be migrated but ensures that no attempt to made to remap the pages would would potentially try to access an already freed anon_vma. Signed-off-by: Mel Gorman Reviewed-by: KAMEZAWA Hiroyuki Reviewed-by: Minchan Kim --- mm/migrate.c | 53 ++++++++++++++++++++++++++++++++++++----------------- 1 files changed, 36 insertions(+), 17 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index b114635..4afd6fe 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -485,7 +485,8 @@ static int fallback_migrate_page(struct address_space *mapping, * < 0 - error code * == 0 - success */ -static int move_to_new_page(struct page *newpage, struct page *page) +static int move_to_new_page(struct page *newpage, struct page *page, + int remap_swapcache) { struct address_space *mapping; int rc; @@ -520,10 +521,12 @@ static int move_to_new_page(struct page *newpage, struct page *page) else rc = fallback_migrate_page(mapping, newpage, page); - if (!rc) - remove_migration_ptes(page, newpage); - else + if (rc) { newpage->mapping = NULL; + } else { + if (remap_swapcache) + remove_migration_ptes(page, newpage); + } unlock_page(newpage); @@ -540,6 +543,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, int rc = 0; int *result = NULL; struct page *newpage = get_new_page(page, private, &result); + int remap_swapcache = 1; int rcu_locked = 0; int charge = 0; struct mem_cgroup *mem = NULL; @@ -601,18 +605,33 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, rcu_read_lock(); rcu_locked = 1; - /* - * If the page has no mappings any more, just bail. An - * unmapped anon page is likely to be freed soon but worse, - * it's possible its anon_vma disappeared between when - * the page was isolated and when we reached here while - * the RCU lock was not held - */ - if (!page_mapped(page)) - goto rcu_unlock; + /* Determine how to safely use anon_vma */ + if (!page_mapped(page)) { + if (!PageSwapCache(page)) + goto rcu_unlock; - anon_vma = page_anon_vma(page); - atomic_inc(&anon_vma->external_refcount); + /* + * We cannot be sure that the anon_vma of an unmapped + * swapcache page is safe to use because we don't + * know in advance if the VMA that this page belonged + * to still exists. If the VMA and others sharing the + * data have been freed, then the anon_vma could + * already be invalid. + * + * To avoid this possibility, swapcache pages get + * migrated but are not remapped when migration + * completes + */ + remap_swapcache = 0; + } else { + /* + * Take a reference count on the anon_vma if the + * page is mapped so that it is guaranteed to + * exist when the page is remapped later + */ + anon_vma = page_anon_vma(page); + atomic_inc(&anon_vma->external_refcount); + } } /* @@ -647,9 +666,9 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, skip_unmap: if (!page_mapped(page)) - rc = move_to_new_page(newpage, page); + rc = move_to_new_page(newpage, page, remap_swapcache); - if (rc) + if (rc && remap_swapcache) remove_migration_ptes(page, page); rcu_unlock: -- 1.6.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/