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Commit 01d8b20d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

mm: simplify anon_vma refcounts 



This patch changes the anon_vma refcount to be 0 when the object is free.
It does this by adding 1 ref to being in use in the anon_vma structure
(iow.  the anon_vma->head list is not empty).

This allows a simpler release scheme without having to check both the
refcount and the list as well as avoids taking a ref for each entry on the
list.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 83813267

include/linux/rmap.h

+9 −2
Original line number Diff line number Diff line
@@ -73,7 +73,13 @@ static inline void get_anon_vma(struct anon_vma *anon_vma) 
	atomic_inc(&anon_vma->refcount);

}



void put_anon_vma(struct anon_vma *);

void __put_anon_vma(struct anon_vma *anon_vma);



static inline void put_anon_vma(struct anon_vma *anon_vma)

{

	if (atomic_dec_and_test(&anon_vma->refcount))

		__put_anon_vma(anon_vma);

}



static inline struct anon_vma *page_anon_vma(struct page *page)

{
@@ -116,7 +122,6 @@ void unlink_anon_vmas(struct vm_area_struct *); 
int anon_vma_clone(struct vm_area_struct *, struct vm_area_struct *);

int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *);

void __anon_vma_link(struct vm_area_struct *);

void anon_vma_free(struct anon_vma *);



static inline void anon_vma_merge(struct vm_area_struct *vma,

				  struct vm_area_struct *next)
@@ -125,6 +130,8 @@ static inline void anon_vma_merge(struct vm_area_struct *vma, 
	unlink_anon_vmas(next);

}



struct anon_vma *page_get_anon_vma(struct page *page);



/*

 * rmap interfaces called when adding or removing pte of page

 */

mm/rmap.c

+28 −48
Original line number Diff line number Diff line
@@ -67,11 +67,24 @@ static struct kmem_cache *anon_vma_chain_cachep; 


static inline struct anon_vma *anon_vma_alloc(void)

{

	return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);

	struct anon_vma *anon_vma;



	anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);

	if (anon_vma) {

		atomic_set(&anon_vma->refcount, 1);

		/*

		 * Initialise the anon_vma root to point to itself. If called

		 * from fork, the root will be reset to the parents anon_vma.

		 */

		anon_vma->root = anon_vma;

	}



	return anon_vma;

}



void anon_vma_free(struct anon_vma *anon_vma)

static inline void anon_vma_free(struct anon_vma *anon_vma)

{

	VM_BUG_ON(atomic_read(&anon_vma->refcount));

	kmem_cache_free(anon_vma_cachep, anon_vma);

}
@@ -133,11 +146,6 @@ int anon_vma_prepare(struct vm_area_struct *vma) 
			if (unlikely(!anon_vma))

				goto out_enomem_free_avc;

			allocated = anon_vma;

			/*

			 * This VMA had no anon_vma yet.  This anon_vma is

			 * the root of any anon_vma tree that might form.

			 */

			anon_vma->root = anon_vma;

		}



		anon_vma_lock(anon_vma);
@@ -156,7 +164,7 @@ int anon_vma_prepare(struct vm_area_struct *vma) 
		anon_vma_unlock(anon_vma);



		if (unlikely(allocated))

			anon_vma_free(allocated);

			put_anon_vma(allocated);

		if (unlikely(avc))

			anon_vma_chain_free(avc);

	}
@@ -241,9 +249,9 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) 
	 */

	anon_vma->root = pvma->anon_vma->root;

	/*

	 * With KSM refcounts, an anon_vma can stay around longer than the

	 * process it belongs to.  The root anon_vma needs to be pinned

	 * until this anon_vma is freed, because the lock lives in the root.

	 * With refcounts, an anon_vma can stay around longer than the

	 * process it belongs to. The root anon_vma needs to be pinned until

	 * this anon_vma is freed, because the lock lives in the root.

	 */

	get_anon_vma(anon_vma->root);

	/* Mark this anon_vma as the one where our new (COWed) pages go. */
@@ -253,7 +261,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) 
	return 0;



 out_error_free_anon_vma:

	anon_vma_free(anon_vma);

	put_anon_vma(anon_vma);

 out_error:

	unlink_anon_vmas(vma);

	return -ENOMEM;
@@ -272,15 +280,11 @@ 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) && !atomic_read(&anon_vma->refcount);

	empty = list_empty(&anon_vma->head);

	anon_vma_unlock(anon_vma);



	if (empty) {

		/* We no longer need the root anon_vma */

		if (anon_vma->root != anon_vma)

			put_anon_vma(anon_vma->root);

		anon_vma_free(anon_vma);

	}

	if (empty)

		put_anon_vma(anon_vma);

}



void unlink_anon_vmas(struct vm_area_struct *vma)
@@ -1486,38 +1490,14 @@ int try_to_munlock(struct page *page) 
		return try_to_unmap_file(page, TTU_MUNLOCK);

}



/*

 * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root

 * if necessary.  Be careful to do all the tests under the lock.  Once

 * we know we are the last user, nobody else can get a reference and we

 * can do the freeing without the lock.

 */

void put_anon_vma(struct anon_vma *anon_vma)

void __put_anon_vma(struct anon_vma *anon_vma)

{

	BUG_ON(atomic_read(&anon_vma->refcount) <= 0);

	if (atomic_dec_and_lock(&anon_vma->refcount, &anon_vma->root->lock)) {

	struct anon_vma *root = anon_vma->root;

		int empty = list_empty(&anon_vma->head);

		int last_root_user = 0;

		int root_empty = 0;



		/*

		 * The refcount on a non-root anon_vma got dropped.  Drop

		 * the refcount on the root and check if we need to free it.

		 */

		if (empty && anon_vma != root) {

			BUG_ON(atomic_read(&root->refcount) <= 0);

			last_root_user = atomic_dec_and_test(&root->refcount);

			root_empty = list_empty(&root->head);

		}

		anon_vma_unlock(anon_vma);

	if (root != anon_vma && atomic_dec_and_test(&root->refcount))

		anon_vma_free(root);



		if (empty) {

	anon_vma_free(anon_vma);

			if (root_empty && last_root_user)

				anon_vma_free(root);

		}

	}

}



#ifdef CONFIG_MIGRATION