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mm: use refcounts for page_lock_anon_vma()

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Convert page_lock_anon_vma() over to use refcounts.  This is done to
prepare for the conversion of anon_vma from spinlock to mutex.

Sadly this inceases the cost of page_lock_anon_vma() from one to two
atomics, a follow up patch addresses this, lets keep that simple for now.

Signed-off-by: Peter Zijlstra <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: David Miller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Russell King <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Namhyung Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Peter Zijlstra 2011-05-24 17:12:10 -07:00 • committed by Linus Torvalds
commit 746b18d421
2 changed files with 31 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

42
mm/rmap.c
View file

@ -337,9 +337,9 @@ 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();
@ -350,30 +350,42 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
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
* freed. But if it has been unmapped, we have no security against
* the anon_vma structure being freed and reused (for another anon_vma:
* SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot
* corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting
* anon_vma->root before page_unlock_anon_vma() is called to unlock.
* freed. But if it has been unmapped, we have no security against the
* anon_vma structure being freed and reused (for another anon_vma:
* SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
* above cannot corrupt).
*/
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;
}
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);
}
/*