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    SubjectRe: [PATCH 2/4] memcg: set page->mapping NULL before uncharge
    On Mon, 29 Sep 2008 19:22:40 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > This patch tries to make page->mapping to be NULL before
    > mem_cgroup_uncharge_cache_page() is called.
    >
    > "page->mapping == NULL" is a good check for "whether the page is still
    > radix-tree or not".
    > This patch also adds BUG_ON() to mem_cgroup_uncharge_cache_page();
    >
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    Looks good to me.

    Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

    > mm/filemap.c | 2 +-
    > mm/memcontrol.c | 1 +
    > mm/migrate.c | 9 +++++++--
    > 3 files changed, 9 insertions(+), 3 deletions(-)
    >
    > Index: mmotm-2.6.27-rc7+/mm/filemap.c
    > ===================================================================
    > --- mmotm-2.6.27-rc7+.orig/mm/filemap.c
    > +++ mmotm-2.6.27-rc7+/mm/filemap.c
    > @@ -116,12 +116,12 @@ void __remove_from_page_cache(struct pag
    > {
    > struct address_space *mapping = page->mapping;
    >
    > - mem_cgroup_uncharge_cache_page(page);
    > radix_tree_delete(&mapping->page_tree, page->index);
    > page->mapping = NULL;
    > mapping->nrpages--;
    > __dec_zone_page_state(page, NR_FILE_PAGES);
    > BUG_ON(page_mapped(page));
    > + mem_cgroup_uncharge_cache_page(page);
    >
    > /*
    > * Some filesystems seem to re-dirty the page even after
    > Index: mmotm-2.6.27-rc7+/mm/memcontrol.c
    > ===================================================================
    > --- mmotm-2.6.27-rc7+.orig/mm/memcontrol.c
    > +++ mmotm-2.6.27-rc7+/mm/memcontrol.c
    > @@ -734,6 +734,7 @@ void mem_cgroup_uncharge_page(struct pag
    > void mem_cgroup_uncharge_cache_page(struct page *page)
    > {
    > VM_BUG_ON(page_mapped(page));
    > + VM_BUG_ON(page->mapping);
    > __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
    > }
    >
    > Index: mmotm-2.6.27-rc7+/mm/migrate.c
    > ===================================================================
    > --- mmotm-2.6.27-rc7+.orig/mm/migrate.c
    > +++ mmotm-2.6.27-rc7+/mm/migrate.c
    > @@ -330,8 +330,6 @@ static int migrate_page_move_mapping(str
    > __inc_zone_page_state(newpage, NR_FILE_PAGES);
    >
    > spin_unlock_irq(&mapping->tree_lock);
    > - if (!PageSwapCache(newpage))
    > - mem_cgroup_uncharge_cache_page(page);
    >
    > return 0;
    > }
    > @@ -341,6 +339,8 @@ static int migrate_page_move_mapping(str
    > */
    > static void migrate_page_copy(struct page *newpage, struct page *page)
    > {
    > + int anon;
    > +
    > copy_highpage(newpage, page);
    >
    > if (PageError(page))
    > @@ -378,8 +378,13 @@ static void migrate_page_copy(struct pag
    > #endif
    > ClearPagePrivate(page);
    > set_page_private(page, 0);
    > + /* page->mapping contains a flag for PageAnon() */
    > + anon = PageAnon(page);
    > page->mapping = NULL;
    >
    > + if (!anon) /* This page was removed from radix-tree. */
    > + mem_cgroup_uncharge_cache_page(page);
    > +
    > /*
    > * If any waiters have accumulated on the new page then
    > * wake them up.
    >


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