On Tue, 23 Mar 2010, Mel Gorman wrote:
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 98eaaf2..6eb1efe 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -603,6 +603,19 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> */
> if (PageAnon(page)) {
> rcu_read_lock();
> +
> + /*
> + * 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_mapcount(page)) {
> + rcu_read_unlock();
> + goto uncharge;
> + }
> +
> rcu_locked = 1;
> anon_vma = page_anon_vma(page);
> atomic_inc(&anon_vma->migrate_refcount);
A way to make this simpler would be to move "rcu_locked = 1" before the
if statement and then do
if (!page_mapcount(page))
goto rcu_unlock;
--
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