mm: convert i_mmap_mutex to rwsem

The i_mmap_mutex is a close cousin of the anon vma lock, both protecting
similar data, one for file backed pages and the other for anon memory.  To
this end, this lock can also be a rwsem.  In addition, there are some
important opportunities to share the lock when there are no tree
modifications.

This conversion is straightforward.  For now, all users take the write
lock.

[sfr@canb.auug.org.au: update fremap.c]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 6 deletions

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index a082709aa427..5eba47f593f8 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -472,12 +472,12 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
 }
 
 /*
- * Hugetlbfs is not reclaimable; therefore its i_mmap_mutex will never
+ * Hugetlbfs is not reclaimable; therefore its i_mmap_rwsem will never
  * be taken from reclaim -- unlike regular filesystems. This needs an
  * annotation because huge_pmd_share() does an allocation under
- * i_mmap_mutex.
+ * i_mmap_rwsem.
  */
-static struct lock_class_key hugetlbfs_i_mmap_mutex_key;
+static struct lock_class_key hugetlbfs_i_mmap_rwsem_key;
 
 static struct inode *hugetlbfs_get_inode(struct super_block *sb,
                                         struct inode *dir,
@@ -495,8 +495,8 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
                 struct hugetlbfs_inode_info *info;
                 inode->i_ino = get_next_ino();
                 inode_init_owner(inode, dir, mode);
-                lockdep_set_class(&inode->i_mapping->i_mmap_mutex,
-                                &hugetlbfs_i_mmap_mutex_key);
+                lockdep_set_class(&inode->i_mapping->i_mmap_rwsem,
+                                &hugetlbfs_i_mmap_rwsem_key);
                 inode->i_mapping->a_ops = &hugetlbfs_aops;
                 inode->i_mapping->backing_dev_info =&hugetlbfs_backing_dev_info;
                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
diff --git a/fs/inode.c b/fs/inode.c
index 2ed95f7caa4f..ad60555b4768 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -346,7 +346,7 @@ void address_space_init_once(struct address_space *mapping)
         memset(mapping, 0, sizeof(*mapping));
         INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
         spin_lock_init(&mapping->tree_lock);
-        mutex_init(&mapping->i_mmap_mutex);
+        init_rwsem(&mapping->i_mmap_rwsem);
         INIT_LIST_HEAD(&mapping->private_list);
         spin_lock_init(&mapping->private_lock);
         mapping->i_mmap = RB_ROOT;