linux-kernel - [PATCH 08/10] mm/mremap: share the i_mmap

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Date:	Fri, 24 Oct 2014 15:06:18 -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 08/10] mm/mremap: share the i_mmap_rwsem

As per the comment in move_ptes(), we only require taking the
anon vma and i_mmap locks to ensure that rmap will always observe
either the old or new ptes, in the case of need_rmap_lock=true.
No modifications to the tree itself, thus share the i_mmap_rwsem.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
XXX: the same *should* apply for the anon vma, as there are
no modifications to the chain.

 mm/mremap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index 84aa36f..a34500c 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -119,7 +119,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 	if (need_rmap_locks) {
 		if (vma->vm_file) {
 			mapping = vma->vm_file->f_mapping;
-			i_mmap_lock_write(mapping);
+			i_mmap_lock_read(mapping);
 		}
 		if (vma->anon_vma) {
 			anon_vma = vma->anon_vma;
@@ -156,7 +156,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 	if (anon_vma)
 		anon_vma_unlock_write(anon_vma);
 	if (mapping)
-		i_mmap_unlock_write(mapping);
+		i_mmap_unlock_read(mapping);
 }
 
 #define LATENCY_LIMIT	(64 * PAGE_SIZE)
-- 
1.8.4.5

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