[RFC] remove page_table_lock in anon_vma_prepare

[Minchan Kim]

As I looked over the page_table_lock, it related to page table not anon_vma

I think anon_vma->lock can protect race against threads.
Do I miss something ?

If I am right, we can remove unnecessary page_table_lock holding
in anon_vma_prepare. We can get performance benefit. 

Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
---
 mm/rmap.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index b5c6e12..65b4877 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -113,14 +113,11 @@ int anon_vma_prepare(struct vm_area_struct *vma)
 		}
 		spin_lock(&anon_vma->lock);
 
-		/* page_table_lock to protect against threads */
-		spin_lock(&mm->page_table_lock);
 		if (likely(!vma->anon_vma)) {
 			vma->anon_vma = anon_vma;
 			list_add_tail(&vma->anon_vma_node, &anon_vma->head);
 			allocated = NULL;
 		}
-		spin_unlock(&mm->page_table_lock);
 
 		spin_unlock(&anon_vma->lock);
 		if (unlikely(allocated))
-- 
1.5.6.5

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