From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 18 Apr 2006 12:00:16 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 5/5] Swapless V2: Revise main migration logic Message-Id: <20060418120016.14419e02.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <20060413235406.15398.42233.sendpatchset@schroedinger.engr.sgi.com> <20060413235432.15398.23912.sendpatchset@schroedinger.engr.sgi.com> <20060414101959.d59ac82d.kamezawa.hiroyu@jp.fujitsu.com> <20060414113455.15fd5162.kamezawa.hiroyu@jp.fujitsu.com> <20060415090639.dde469e8.kamezawa.hiroyu@jp.fujitsu.com> <20060417091830.bca60006.kamezawa.hiroyu@jp.fujitsu.com> <20060418090439.3e2f0df4.kamezawa.hiroyu@jp.fujitsu.com> <20060418094212.3ece222f.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: akpm@osdl.org, hugh@veritas.com, linux-kernel@vger.kernel.org, lee.schermerhorn@hp.com, linux-mm@kvack.org, taka@valinux.co.jp, marcelo.tosatti@cyclades.com List-ID: On Mon, 17 Apr 2006 18:57:40 -0700 (PDT) Christoph Lameter wrote: > On Tue, 18 Apr 2006, KAMEZAWA Hiroyuki wrote: > > > BTW, when copying mm, mm->mmap_sem is held. Is mm->mmap_sem is not held while > > page migraion now ? I'm sorry I can't catch up all changes. > > or Is this needed for lazy migration (migration-on-fault) ? > > mmap_sem must be held during page migration due to the way we retrieve the > anonymous vma. > > I think you would want to get rid of that requirement for the hotplug > remove. yes. > But how do we reliably get to the anon_vma of the page without mmap_sem? > > I think following patch will help. but this increases complexity... -Kame = hold anon_vma->lock under migration. While migration, page_mapcount(page) goes down to 0 and page->mapping is valid. This breaks assumptions around page_mapcount() and page->mapping. (See rmap.c, page_remove_rmap()) If mmap->sem is held while migration, there is no problem. But if mmap->sem is not held, this is a race. This patch locks anon_vma under migration. Signed-Off-By: KAMEZAWA Hiroyuki Index: Christoph-NewMigrationV2/mm/migrate.c =================================================================== --- Christoph-NewMigrationV2.orig/mm/migrate.c +++ Christoph-NewMigrationV2/mm/migrate.c @@ -178,6 +178,20 @@ out: } /* + * When mmap->sem is not held, we have to guarantee anon_vma is not freed. + */ +static void migrate_lock_anon_vma(struct page *page) +{ + unsigned long mapping; + struct anon_vma *anon_vma; + struct vm_area_struct *vma; + + if (PageAnon(page)) + page_lock_anon_vma(page); + /* remove migration ptes will unlock */ +} + +/* * Get rid of all migration entries and replace them by * references to the indicated page. * @@ -196,10 +210,9 @@ static void remove_migration_ptes(struct return; /* - * We hold the mmap_sem lock. So no need to call page_lock_anon_vma. + * anon_vma is preserved and locked while migration. */ anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON); - spin_lock(&anon_vma->lock); list_for_each_entry(vma, &anon_vma->head, anon_vma_node) remove_migration_pte(vma, page_address_in_vma(new, vma), @@ -371,6 +384,7 @@ int migrate_page(struct page *newpage, s BUG_ON(PageWriteback(page)); /* Writeback must be complete */ + migrate_lock_anon_vma(page); rc = migrate_page_remove_references(newpage, page, page_mapping(page) ? 2 : 1); @@ -378,7 +392,6 @@ int migrate_page(struct page *newpage, s remove_migration_ptes(page, page); return rc; } - migrate_page_copy(newpage, page); remove_migration_ptes(page, newpage); return 0; Index: Christoph-NewMigrationV2/mm/rmap.c =================================================================== --- Christoph-NewMigrationV2.orig/mm/rmap.c +++ Christoph-NewMigrationV2/mm/rmap.c @@ -160,7 +160,7 @@ void anon_vma_unlink(struct vm_area_stru empty = list_empty(&anon_vma->head); spin_unlock(&anon_vma->lock); - if (empty) + if (empty && !anon_vma->async_refernece) anon_vma_free(anon_vma); } @@ -717,7 +717,13 @@ static int try_to_unmap_anon(struct page struct vm_area_struct *vma; int ret = SWAP_AGAIN; - anon_vma = page_lock_anon_vma(page); + if (migration) { /* anon_vma->lock is held under migration */ + unsigned long mapping; + mapping = (unsigned long)page->mapping - PAGE_MAPPING_ANON; + anon_vma = (struct anon_vma *)mapping; + } else { + anon_vma = page_lock_anon_vma(page); + } if (!anon_vma) return ret; @@ -726,7 +732,8 @@ static int try_to_unmap_anon(struct page if (ret == SWAP_FAIL || !page_mapped(page)) break; } - spin_unlock(&anon_vma->lock); + if (!migration) + spin_unlock(&anon_vma->lock); return ret; } -- 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