linux-kernel - [PATCH 04/10] mm/rmap: share the i_mmap

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Message-Id: <1414697657-1678-5-git-send-email-dave@stgolabs.net>
Date:	Thu, 30 Oct 2014 12:34:11 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	akpm@...ux-foundation.org
Cc:	hughd@...gle.com, riel@...hat.com, mgorman@...e.de,
	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, dbueso@...e.de, linux-mm@...ck.org,
	Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH 04/10] 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@...e.de>
Acked-by: Rik van Riel <riel@...hat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...el.linux.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 648a77e..552a9fc 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 e0c0e90..7ab830b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1688,7 +1688,8 @@ 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);
 
@@ -1709,9 +1710,8 @@ 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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