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, 8 insertions, 8 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);
 }
 
 /*