[PATCH 04/10] mm/rmap: share the i_mmap_rwsem

[Davidlohr Bueso <dave@stgolabs.net>]

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>
---
 include/linux/fs.h | 10 ++++++++++
 mm/rmap.c          |  6 +++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b183792..1059be0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -465,6 +465,16 @@ 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 f234bc6..a77726f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1674,7 +1674,8 @@ 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);
 
@@ -1695,9 +1696,8 @@ 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;
 }
 
-- 
1.8.4.5

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