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 <dbueso@suse.de>
Acked-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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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;
 }