On Fri, 2 Apr 2010 17:02:37 +0100
Mel Gorman <mel@xxxxxxxxx> wrote:
> For clarity of review, KSM and page migration have separate refcounts on
> the anon_vma. While clear, this is a waste of memory. This patch gets
> KSM and page migration to share their toys in a spirit of harmony.
>
> ...
>
> @@ -26,11 +26,17 @@
> */
> struct anon_vma {
> spinlock_t lock; /* Serialize access to vma list */
> -#ifdef CONFIG_KSM
> - atomic_t ksm_refcount;
> -#endif
> -#ifdef CONFIG_MIGRATION
> - atomic_t migrate_refcount;
> +#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
> +
> + /*
> + * The external_refcount is taken by either KSM or page migration
> + * to take a reference to an anon_vma when there is no
> + * guarantee that the vma of page tables will exist for
> + * the duration of the operation. A caller that takes
> + * the reference is responsible for clearing up the
> + * anon_vma if they are the last user on release
> + */
> + atomic_t external_refcount;
> #endif
hah.
> @@ -653,7 +653,7 @@ skip_unmap:
> 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)) {
> + if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) {
> int empty = list_empty(&anon_vma->head);
> spin_unlock(&anon_vma->lock);
> if (empty)
So we now _do_ test ksm_refcount. Perhaps that fixed a bug added in [1/14]
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 578d0fe..af35b75 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -248,8 +248,7 @@ static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
> list_del(&anon_vma_chain->same_anon_vma);
>
> /* We must garbage collect the anon_vma if it's empty */
> - empty = list_empty(&anon_vma->head) && !ksm_refcount(anon_vma) &&
> - !migrate_refcount(anon_vma);
> + empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma);
> spin_unlock(&anon_vma->lock);
>
> if (empty)
> @@ -273,8 +272,7 @@ static void anon_vma_ctor(void *data)
> struct anon_vma *anon_vma = data;
>
> spin_lock_init(&anon_vma->lock);
> - ksm_refcount_init(anon_vma);
> - migrate_refcount_init(anon_vma);
> + anonvma_external_refcount_init(anon_vma);
What a mouthful. Can we do s/external_//g?
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>