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authorRik van Riel <riel@redhat.com>2010-08-09 17:18:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-09 20:44:55 -0700
commit012f18004da33ba672e3c60838cc4898126174d3 (patch)
tree990382f9f8c0d885463ac9195b8e9a18043f716d /mm/mmap.c
parent5c341ee1dfc8fe69d66b1c8b19e463c6d7201ae1 (diff)
downloadvexpress-lsk-012f18004da33ba672e3c60838cc4898126174d3.tar.gz
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>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c30
1 files changed, 22 insertions, 8 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index f5db18decc2..fb89360a212 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -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);
}