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>

4 files changed, 25 insertions, 25 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bfe1f4780644..f3f41d242e25 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -7,7 +7,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
-#include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <linux/memcontrol.h>
 
 /*
@@ -25,8 +25,8 @@
  * pointing to this anon_vma once its vma list is empty.
  */
 struct anon_vma {
-        struct anon_vma *root;  /* Root of this anon_vma tree */
-        struct mutex mutex;     /* Serialize access to vma list */
+        struct anon_vma *root;          /* Root of this anon_vma tree */
+        struct rw_semaphore rwsem;      /* W: modification, R: walking the list */
         /*
          * The refcount is taken on an anon_vma when there is no
          * guarantee that the vma of page tables will exist for
@@ -64,7 +64,7 @@ struct anon_vma_chain {
         struct vm_area_struct *vma;
         struct anon_vma *anon_vma;
         struct list_head same_vma;   /* locked by mmap_sem & page_table_lock */
-        struct rb_node rb;                      /* locked by anon_vma->mutex */
+        struct rb_node rb;                      /* locked by anon_vma->rwsem */
         unsigned long rb_subtree_last;
 #ifdef CONFIG_DEBUG_VM_RB
         unsigned long cached_vma_start, cached_vma_last;
@@ -108,24 +108,24 @@ static inline void vma_lock_anon_vma(struct vm_area_struct *vma)
 {
         struct anon_vma *anon_vma = vma->anon_vma;
         if (anon_vma)
-                mutex_lock(&anon_vma->root->mutex);
+                down_write(&anon_vma->root->rwsem);
 }
 
 static inline void vma_unlock_anon_vma(struct vm_area_struct *vma)
 {
         struct anon_vma *anon_vma = vma->anon_vma;
         if (anon_vma)
-                mutex_unlock(&anon_vma->root->mutex);
+                up_write(&anon_vma->root->rwsem);
 }
 
 static inline void anon_vma_lock(struct anon_vma *anon_vma)
 {
-        mutex_lock(&anon_vma->root->mutex);
+        down_write(&anon_vma->root->rwsem);
 }
 
 static inline void anon_vma_unlock(struct anon_vma *anon_vma)
 {
-        mutex_unlock(&anon_vma->root->mutex);
+        up_write(&anon_vma->root->rwsem);
 }
 
 /*
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 711baf84b153..acd37fe55eb7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1292,7 +1292,7 @@ static int __split_huge_page_splitting(struct page *page,
                  * We can't temporarily set the pmd to null in order
                  * to split it, the pmd must remain marked huge at all
                  * times or the VM won't take the pmd_trans_huge paths
-                 * and it won't wait on the anon_vma->root->mutex to
+                 * and it won't wait on the anon_vma->root->rwsem to
                  * serialize against split_huge_page*.
                  */
                 pmdp_splitting_flush(vma, address, pmd);
@@ -1495,7 +1495,7 @@ static int __split_huge_page_map(struct page *page,
         return ret;
 }
 
-/* must be called with anon_vma->root->mutex hold */
+/* must be called with anon_vma->root->rwsem held */
 static void __split_huge_page(struct page *page,
                               struct anon_vma *anon_vma)
 {
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))
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.