Messages in this thread | | | Date | Wed, 21 Apr 2010 11:49:20 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 01/14] mm,migration: Take a reference to the anon_vma before migrating |
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On Tue, 20 Apr 2010 22:01:03 +0100 Mel Gorman <mel@csn.ul.ie> wrote:
> rmap_walk_anon() does not use page_lock_anon_vma() for looking up and > locking an anon_vma and it does not appear to have sufficient locking to > ensure the anon_vma does not disappear from under it. > > This patch copies an approach used by KSM to take a reference on the > anon_vma while pages are being migrated. This should prevent rmap_walk() > running into nasty surprises later because anon_vma has been freed. > > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Hmm, a nitpick..
> static inline struct anon_vma *page_anon_vma(struct page *page) > { > diff --git a/mm/migrate.c b/mm/migrate.c > index 5938db5..b768a1d 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -543,6 +543,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, > int rcu_locked = 0; > int charge = 0; > struct mem_cgroup *mem = NULL; > + struct anon_vma *anon_vma = NULL; > > if (!newpage) > return -ENOMEM; > @@ -599,6 +600,8 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, > if (PageAnon(page)) { > rcu_read_lock(); > rcu_locked = 1; > + anon_vma = page_anon_vma(page); > + atomic_inc(&anon_vma->migrate_refcount); > } > > /* > @@ -638,6 +641,15 @@ skip_unmap: > if (rc) > remove_migration_ptes(page, page); > rcu_unlock: > + > + /* Drop an anon_vma reference if we took one */ > + if (anon_vma && atomic_dec_and_lock(&anon_vma->migrate_refcount, &anon_vma->lock)) { > + int empty = list_empty(&anon_vma->head); > + spin_unlock(&anon_vma->lock); > + if (empty) > + anon_vma_free(anon_vma); > + } > +
Hmm. Can't we move this part to mm/rmap.c ?
as anon_vma_drop_external_reference() or some.
Thanks, -Kame
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