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>
diff --git a/mm/mmap.c b/mm/mmap.c
index f5db18de..fb89360 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -506,6 +506,7 @@
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 @@
}
}
+ /*
+ * 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 @@
__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 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 @@
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 @@
*
* 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);
}