[PATCH 4/5] mm/rmap: share the i_mmap_rwsem

[Davidlohr Bueso <davidlohr@hp.com>]

Similarly to rmap_walk_anon() and collect_procs_anon(),
there is opportunity to share the lock in rmap_walk_file()
and collect_procs_file() for file backed pages.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
---
 include/linux/fs.h  | 10 ++++++++++
 mm/memory-failure.c |  4 ++--
 mm/rmap.c           |  4 ++--
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 60a1d7d..4c2c228 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -467,6 +467,16 @@ 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/memory-failure.c b/mm/memory-failure.c
index 1389a28..acbcd8e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -434,7 +434,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
 	struct task_struct *tsk;
 	struct address_space *mapping = page->mapping;
 
-	i_mmap_lock_write(mapping);
+	i_mmap_lock_read(mapping);
 	read_lock(&tasklist_lock);
 	for_each_process(tsk) {
 		pgoff_t pgoff = page_pgoff(page);
@@ -456,7 +456,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
 		}
 	}
 	read_unlock(&tasklist_lock);
-	i_mmap_unlock_write(mapping);
+	i_mmap_unlock_read(mapping);
 }
 
 /*
diff --git a/mm/rmap.c b/mm/rmap.c
index 9a56e4f..5841dcb 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1685,7 +1685,7 @@ 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);
 
@@ -1708,7 +1708,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 	ret = rwc->file_nonlinear(page, mapping, rwc->arg);
 
 done:
-	i_mmap_unlock_write(mapping);
+	i_mmap_unlock_read(mapping);
 	return ret;
 }
 
-- 
1.8.1.4

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