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

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
...@@ -104,24 +104,24 @@ static inline void vma_lock_anon_vma(struct vm_area_struct *vma) ...@@ -104,24 +104,24 @@ static inline void vma_lock_anon_vma(struct vm_area_struct *vma)
{ {
struct anon_vma *anon_vma = vma->anon_vma; struct anon_vma *anon_vma = vma->anon_vma;
if (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) static inline void vma_unlock_anon_vma(struct vm_area_struct *vma)
{ {
struct anon_vma *anon_vma = vma->anon_vma; struct anon_vma *anon_vma = vma->anon_vma;
if (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) 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) static inline void anon_vma_unlock(struct anon_vma *anon_vma)
{ {
spin_unlock(&anon_vma->lock); spin_unlock(&anon_vma->root->lock);
} }
/* /*
......
...@@ -325,7 +325,7 @@ static void drop_anon_vma(struct rmap_item *rmap_item) ...@@ -325,7 +325,7 @@ static void drop_anon_vma(struct rmap_item *rmap_item)
{ {
struct anon_vma *anon_vma = rmap_item->anon_vma; 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); int empty = list_empty(&anon_vma->head);
anon_vma_unlock(anon_vma); anon_vma_unlock(anon_vma);
if (empty) if (empty)
......
...@@ -682,7 +682,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, ...@@ -682,7 +682,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
rcu_unlock: rcu_unlock:
/* Drop an anon_vma reference if we took one */ /* 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); int empty = list_empty(&anon_vma->head);
anon_vma_unlock(anon_vma); anon_vma_unlock(anon_vma);
if (empty) if (empty)
......
...@@ -506,6 +506,7 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start, ...@@ -506,6 +506,7 @@ int vma_adjust(struct vm_area_struct *vma, unsigned long start,
struct vm_area_struct *importer = NULL; struct vm_area_struct *importer = NULL;
struct address_space *mapping = NULL; struct address_space *mapping = NULL;
struct prio_tree_root *root = NULL; struct prio_tree_root *root = NULL;
struct anon_vma *anon_vma = NULL;
struct file *file = vma->vm_file; struct file *file = vma->vm_file;
long adjust_next = 0; long adjust_next = 0;
int remove_next = 0; int remove_next = 0;
...@@ -578,6 +579,17 @@ again: remove_next = 1 + (end > next->vm_end); ...@@ -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) { if (root) {
flush_dcache_mmap_lock(mapping); flush_dcache_mmap_lock(mapping);
vma_prio_tree_remove(vma, root); vma_prio_tree_remove(vma, root);
...@@ -617,6 +629,8 @@ again: remove_next = 1 + (end > next->vm_end); ...@@ -617,6 +629,8 @@ again: remove_next = 1 + (end > next->vm_end);
__insert_vm_struct(mm, insert); __insert_vm_struct(mm, insert);
} }
if (anon_vma)
anon_vma_unlock(anon_vma);
if (mapping) if (mapping)
spin_unlock(&mapping->i_mmap_lock); spin_unlock(&mapping->i_mmap_lock);
...@@ -2470,23 +2484,23 @@ static DEFINE_MUTEX(mm_all_locks_mutex); ...@@ -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) 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 * The LSB of head.next can't change from under us
* because we hold the mm_all_locks_mutex. * 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 * 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. * the same anon_vma we won't take it again.
* *
* No need of atomic instructions here, head.next * No need of atomic instructions here, head.next
* can't change from under us thanks to the * can't change from under us thanks to the
* anon_vma->lock. * anon_vma->root->lock.
*/ */
if (__test_and_set_bit(0, (unsigned long *) if (__test_and_set_bit(0, (unsigned long *)
&anon_vma->head.next)) &anon_vma->root->head.next))
BUG(); BUG();
} }
} }
...@@ -2577,7 +2591,7 @@ int mm_take_all_locks(struct mm_struct *mm) ...@@ -2577,7 +2591,7 @@ int mm_take_all_locks(struct mm_struct *mm)
static void vm_unlock_anon_vma(struct anon_vma *anon_vma) 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 * The LSB of head.next can't change to 0 from under
* us because we hold the mm_all_locks_mutex. * us because we hold the mm_all_locks_mutex.
...@@ -2588,10 +2602,10 @@ static void vm_unlock_anon_vma(struct anon_vma *anon_vma) ...@@ -2588,10 +2602,10 @@ static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
* *
* No need of atomic instructions here, head.next * No need of atomic instructions here, head.next
* can't change from under us until we release the * 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 *) if (!__test_and_clear_bit(0, (unsigned long *)
&anon_vma->head.next)) &anon_vma->root->head.next))
BUG(); BUG();
anon_vma_unlock(anon_vma); anon_vma_unlock(anon_vma);
} }
......
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