2010-11-26 15:07:36

by Peter Zijlstra

Subject: [PATCH 07/21] mm: Use refcounts for page_lock_anon_vma()

Convert page_lock_anon_vma() over to use refcounts. This is
done for each of convertion of anon_vma from spinlock to mutex.

Signed-off-by: Peter Zijlstra <[email protected]>
---
mm/rmap.c | 34 ++++++++++++++++++++++++----------
1 file changed, 24 insertions(+), 10 deletions(-)

Index: linux-2.6/mm/rmap.c
===================================================================
--- linux-2.6.orig/mm/rmap.c
+++ linux-2.6/mm/rmap.c
@@ -332,9 +332,9 @@ void __init anon_vma_init(void)
* that the anon_vma pointer from page->mapping is valid if there is a
* mapcount, we can dereference the anon_vma after observing those.
*/
-struct anon_vma *page_lock_anon_vma(struct page *page)
+struct anon_vma *page_get_anon_vma(struct page *page)
{
- struct anon_vma *anon_vma, *root_anon_vma;
+ struct anon_vma *anon_vma = NULL;
unsigned long anon_mapping;

rcu_read_lock();
@@ -345,8 +345,10 @@ struct anon_vma *page_lock_anon_vma(stru
goto out;

anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
- root_anon_vma = ACCESS_ONCE(anon_vma->root);
- spin_lock(&root_anon_vma->lock);
+ if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+ anon_vma = NULL;
+ goto out;
+ }

/*
* If this page is still mapped, then its anon_vma cannot have been
@@ -356,19 +358,31 @@ struct anon_vma *page_lock_anon_vma(stru
* corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting
* anon_vma->root before page_unlock_anon_vma() is called to unlock.
*/
- if (page_mapped(page))
- return anon_vma;
-
- spin_unlock(&root_anon_vma->lock);
+ if (!page_mapped(page)) {
+ put_anon_vma(anon_vma);
+ anon_vma = NULL;
+ goto out;
+ }
out:
rcu_read_unlock();
- return NULL;
+
+ return anon_vma;
+}
+
+struct anon_vma *page_lock_anon_vma(struct page *page)
+{
+ struct anon_vma *anon_vma = page_get_anon_vma(page);
+
+ if (anon_vma)
+ anon_vma_lock(anon_vma);
+
+ return anon_vma;
}

void page_unlock_anon_vma(struct anon_vma *anon_vma)
{
anon_vma_unlock(anon_vma);
- rcu_read_unlock();
+ put_anon_vma(anon_vma);
}

/*

2010-11-29 02:40:56

by Kamezawa Hiroyuki

Subject: Re: [PATCH 07/21] mm: Use refcounts for page_lock_anon_vma()

On Fri, 26 Nov 2010 15:38:50 +0100
Peter Zijlstra <[email protected]> wrote:

> Convert page_lock_anon_vma() over to use refcounts. This is
> done for each of convertion of anon_vma from spinlock to mutex.
>
> Signed-off-by: Peter Zijlstra <[email protected]>

Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>

Does this patch affect only page_referenced() and try_to_unmap() ?

Thanks,
-Kame

2010-11-29 20:41:50

by Peter Zijlstra

Subject: Re: [PATCH 07/21] mm: Use refcounts for page_lock_anon_vma()

On Mon, 2010-11-29 at 11:35 +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 26 Nov 2010 15:38:50 +0100
> Peter Zijlstra <[email protected]> wrote:
>
> > Convert page_lock_anon_vma() over to use refcounts. This is
> > done for each of convertion of anon_vma from spinlock to mutex.
> >
> > Signed-off-by: Peter Zijlstra <[email protected]>
>
> Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
>
> Does this patch affect only page_referenced() and try_to_unmap() ?

git grep page_lock_anon_vma reveals that
mm/memory-failure.c:collect_procs_anon() is also affected.

2010-11-30 01:21:13

by KOSAKI Motohiro

Subject: Re: [PATCH 07/21] mm: Use refcounts for page_lock_anon_vma()

> On Fri, 26 Nov 2010 15:38:50 +0100
> Peter Zijlstra <[email protected]> wrote:
>
> > Convert page_lock_anon_vma() over to use refcounts. This is
> > done for each of convertion of anon_vma from spinlock to mutex.
> >
> > Signed-off-by: Peter Zijlstra <[email protected]>
>
> Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
>
> Does this patch affect only page_referenced() and try_to_unmap() ?

I like this conversion too.
Reviewed-by: KOSAKI Motohiro <[email protected]>