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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: Rik van Riel <riel@redhat.com>
Tested-by: Larry Woodman <lwoodman@redhat.com>
Acked-by: Larry Woodman <lwoodman@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rik van Riel 2010-08-09 17:18:40 -07:00 committed by Linus Torvalds
parent 5c341ee1df
commit 012f18004d
4 changed files with 28 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/rmap.h
View File

@ -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);
}
/*

2
mm/ksm.c
View File

@ -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)

2
mm/migrate.c
View File

@ -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)

30
mm/mmap.c
View File

@ -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);
}