mm/rmap: Convert the struct anon_vma::mutex to an rwsem

Convert the struct anon_vma::mutex to an rwsem, which will help
in solving a page-migration scalability problem. (Addressed in
a separate patch.)

The conversion is simple and straightforward: in every case
where we mutex_lock()ed we'll now down_write().

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Turner <pjt@google.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>

1 files changed, 4 insertions, 4 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 9a796c41e7d9..88408632da66 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2561,15 +2561,15 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
                  * The LSB of head.next can't change from under us
                  * because we hold the mm_all_locks_mutex.
                  */
-                mutex_lock_nest_lock(&anon_vma->root->mutex, &mm->mmap_sem);
+                down_write(&anon_vma->root->rwsem);
                 /*
                  * We can safely modify head.next after taking the
-                 * anon_vma->root->mutex. If some other vma in this mm shares
+                 * anon_vma->root->rwsem. 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->root->mutex.
+                 * anon_vma->root->rwsem.
                  */
                 if (__test_and_set_bit(0, (unsigned long *)
                                        &anon_vma->root->rb_root.rb_node))
@@ -2671,7 +2671,7 @@ 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->root->mutex.
+                 * anon_vma->root->rwsem.
                  */
                 if (!__test_and_clear_bit(0, (unsigned long *)
                                           &anon_vma->root->rb_root.rb_node))