Commit 012f1800 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

mm: always lock the root (oldest) anon_vma 



Always (and only) lock the root (oldest) anon_vma whenever we do something
in an anon_vma.  The recently introduced anon_vma scalability is due to
the rmap code scanning only the VMAs that need to be scanned.  Many common
operations still took the anon_vma lock on the root anon_vma, so always
taking that lock is not expected to introduce any scalability issues.

However, always taking the same lock does mean we only need to take one
lock, which means rmap_walk on pages from any anon_vma in the vma is
excluded from occurring during an munmap, expand_stack or other operation
that needs to exclude rmap_walk and similar functions.

Also add the proper locking to vma_adjust.

Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Tested-by: default avatarLarry Woodman <lwoodman@redhat.com>
Acked-by: default avatarLarry Woodman <lwoodman@redhat.com>
Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5c341ee1

include/linux/rmap.h

+4 −4
Original line number Diff line number Diff line
@@ -104,24 +104,24 @@ static inline void vma_lock_anon_vma(struct vm_area_struct *vma) 
{

	struct anon_vma *anon_vma = vma->anon_vma;

	if (anon_vma)

		spin_lock(&anon_vma->lock);

		spin_lock(&anon_vma->root->lock);

}



static inline void vma_unlock_anon_vma(struct vm_area_struct *vma)

{

	struct anon_vma *anon_vma = vma->anon_vma;

	if (anon_vma)

		spin_unlock(&anon_vma->lock);

		spin_unlock(&anon_vma->root->lock);

}



static inline void anon_vma_lock(struct anon_vma *anon_vma)

{

	spin_lock(&anon_vma->lock);

	spin_lock(&anon_vma->root->lock);

}



static inline void anon_vma_unlock(struct anon_vma *anon_vma)

{

	spin_unlock(&anon_vma->lock);

	spin_unlock(&anon_vma->root->lock);

}



/*

mm/ksm.c

+1 −1
Original line number Diff line number Diff line
@@ -325,7 +325,7 @@ static void drop_anon_vma(struct rmap_item *rmap_item) 
{

	struct anon_vma *anon_vma = rmap_item->anon_vma;



	if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) {

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

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

		anon_vma_unlock(anon_vma);

		if (empty)

mm/migrate.c

+1 −1
Original line number Diff line number Diff line
@@ -682,7 +682,7 @@ skip_unmap: 
rcu_unlock:



	/* Drop an anon_vma reference if we took one */

	if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) {

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

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

		anon_vma_unlock(anon_vma);

		if (empty)

mm/mmap.c

+22 −8
Original line number Diff line number Diff line
@@ -506,6 +506,7 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start, 
	struct vm_area_struct *importer = NULL;

	struct address_space *mapping = NULL;

	struct prio_tree_root *root = NULL;

	struct anon_vma *anon_vma = NULL;

	struct file *file = vma->vm_file;

	long adjust_next = 0;

	int remove_next = 0;
@@ -578,6 +579,17 @@ again: remove_next = 1 + (end > next->vm_end); 
		}

	}



	/*

	 * When changing only vma->vm_end, we don't really need anon_vma

	 * lock. This is a fairly rare case by itself, but the anon_vma

	 * lock may be shared between many sibling processes.  Skipping

	 * the lock for brk adjustments makes a difference sometimes.

	 */

	if (vma->anon_vma && (insert || importer || start != vma->vm_start)) {

		anon_vma = vma->anon_vma;

		anon_vma_lock(anon_vma);

	}



	if (root) {

		flush_dcache_mmap_lock(mapping);

		vma_prio_tree_remove(vma, root);
@@ -617,6 +629,8 @@ again: remove_next = 1 + (end > next->vm_end); 
		__insert_vm_struct(mm, insert);

	}



	if (anon_vma)

		anon_vma_unlock(anon_vma);

	if (mapping)

		spin_unlock(&mapping->i_mmap_lock);
@@ -2470,23 +2484,23 @@ static DEFINE_MUTEX(mm_all_locks_mutex); 


static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)

{

	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {

	if (!test_bit(0, (unsigned long *) &anon_vma->root->head.next)) {

		/*

		 * The LSB of head.next can't change from under us

		 * because we hold the mm_all_locks_mutex.

		 */

		spin_lock_nest_lock(&anon_vma->lock, &mm->mmap_sem);

		spin_lock_nest_lock(&anon_vma->root->lock, &mm->mmap_sem);

		/*

		 * We can safely modify head.next after taking the

		 * anon_vma->lock. If some other vma in this mm shares

		 * anon_vma->root->lock. If some other vma in this mm shares

		 * the same anon_vma we won't take it again.

		 *

		 * No need of atomic instructions here, head.next

		 * can't change from under us thanks to the

		 * anon_vma->lock.

		 * anon_vma->root->lock.

		 */

		if (__test_and_set_bit(0, (unsigned long *)

				       &anon_vma->head.next))

				       &anon_vma->root->head.next))

			BUG();

	}

}
@@ -2577,7 +2591,7 @@ out_unlock: 


static void vm_unlock_anon_vma(struct anon_vma *anon_vma)

{

	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {

	if (test_bit(0, (unsigned long *) &anon_vma->root->head.next)) {

		/*

		 * The LSB of head.next can't change to 0 from under

		 * us because we hold the mm_all_locks_mutex.
@@ -2588,10 +2602,10 @@ static void vm_unlock_anon_vma(struct anon_vma *anon_vma) 
		 *

		 * No need of atomic instructions here, head.next

		 * can't change from under us until we release the

		 * anon_vma->lock.

		 * anon_vma->root->lock.

		 */

		if (!__test_and_clear_bit(0, (unsigned long *)

					  &anon_vma->head.next))

					  &anon_vma->root->head.next))

			BUG();

		anon_vma_unlock(anon_vma);

	}

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