mm/rmap: share the i_mmap_rwsem

Similarly to the anon memory counterpart, we can share the mapping's lock
ownership as the interval tree is not modified when doing doing the walk,
only the file page.

Signed-off-by: Davidlohr Bueso <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: "Kirill A. Shutemov" <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 13 insertions, 3 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6abcd0b72ae0..1d1838de6882 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -478,6 +478,16 @@ static inline void i_mmap_unlock_write(struct address_space *mapping)
 	up_write(&mapping->i_mmap_rwsem);
 }
 
+static inline void i_mmap_lock_read(struct address_space *mapping)
+{
+	down_read(&mapping->i_mmap_rwsem);
+}
+
+static inline void i_mmap_unlock_read(struct address_space *mapping)
+{
+	up_read(&mapping->i_mmap_rwsem);
+}
+
 /*
  * Might pages of this file be mapped into userspace?
  */
diff --git a/mm/rmap.c b/mm/rmap.c
index 18247f89f1a8..14ad2b3b0f54 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1690,7 +1690,8 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 
 	if (!mapping)
 		return ret;
-	i_mmap_lock_write(mapping);
+
+	i_mmap_lock_read(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
 
@@ -1711,9 +1712,8 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 		goto done;
 
 	ret = rwc->file_nonlinear(page, mapping, rwc->arg);
-
 done:
-	i_mmap_unlock_write(mapping);
+	i_mmap_unlock_read(mapping);
 	return ret;
 }