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, 11 insertions, 11 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 2ee1ef0f317b..6e3ee3b82798 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -24,7 +24,7 @@
  *   mm->mmap_sem
  *     page->flags PG_locked (lock_page)
  *       mapping->i_mmap_mutex
- *         anon_vma->mutex
+ *         anon_vma->rwsem
  *           mm->page_table_lock or pte_lock
  *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
  *             swap_lock (in swap_duplicate, swap_info_get)
@@ -37,7 +37,7 @@
  *                           in arch-dependent flush_dcache_mmap_lock,
  *                           within bdi.wb->list_lock in __sync_single_inode)
  *
- * anon_vma->mutex,mapping->i_mutex      (memory_failure, collect_procs_anon)
+ * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
  *   ->tasklist_lock
  *     pte map lock
  */
@@ -103,7 +103,7 @@ static inline void anon_vma_free(struct anon_vma *anon_vma)
          * LOCK should suffice since the actual taking of the lock must
          * happen _before_ what follows.
          */
-        if (mutex_is_locked(&anon_vma->root->mutex)) {
+        if (rwsem_is_locked(&anon_vma->root->rwsem)) {
                 anon_vma_lock(anon_vma);
                 anon_vma_unlock(anon_vma);
         }
@@ -219,9 +219,9 @@ static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct
         struct anon_vma *new_root = anon_vma->root;
         if (new_root != root) {
                 if (WARN_ON_ONCE(root))
-                        mutex_unlock(&root->mutex);
+                        up_write(&root->rwsem);
                 root = new_root;
-                mutex_lock(&root->mutex);
+                down_write(&root->rwsem);
         }
         return root;
 }
@@ -229,7 +229,7 @@ static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct
 static inline void unlock_anon_vma_root(struct anon_vma *root)
 {
         if (root)
-                mutex_unlock(&root->mutex);
+                up_write(&root->rwsem);
 }
 
 /*
@@ -349,7 +349,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
         /*
          * Iterate the list once more, it now only contains empty and unlinked
          * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
-         * needing to acquire the anon_vma->root->mutex.
+         * needing to write-acquire the anon_vma->root->rwsem.
          */
         list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
                 struct anon_vma *anon_vma = avc->anon_vma;
@@ -365,7 +365,7 @@ static void anon_vma_ctor(void *data)
 {
         struct anon_vma *anon_vma = data;
 
-        mutex_init(&anon_vma->mutex);
+        init_rwsem(&anon_vma->rwsem);
         atomic_set(&anon_vma->refcount, 0);
         anon_vma->rb_root = RB_ROOT;
 }
@@ -457,14 +457,14 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
 
         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
         root_anon_vma = ACCESS_ONCE(anon_vma->root);
-        if (mutex_trylock(&root_anon_vma->mutex)) {
+        if (down_write_trylock(&root_anon_vma->rwsem)) {
                 /*
                  * If the page is still mapped, then this anon_vma is still
                  * its anon_vma, and holding the mutex ensures that it will
                  * not go away, see anon_vma_free().
                  */
                 if (!page_mapped(page)) {
-                        mutex_unlock(&root_anon_vma->mutex);
+                        up_write(&root_anon_vma->rwsem);
                         anon_vma = NULL;
                 }
                 goto out;
@@ -1299,7 +1299,7 @@ out_mlock:
         /*
          * We need mmap_sem locking, Otherwise VM_LOCKED check makes
          * unstable result and race. Plus, We can't wait here because
-         * we now hold anon_vma->mutex or mapping->i_mmap_mutex.
+         * we now hold anon_vma->rwsem or mapping->i_mmap_mutex.
          * if trylock failed, the page remain in evictable lru and later
          * vmscan could retry to move the page to unevictable lru if the
          * page is actually mlocked.