linux-kernel - [RFC][PATCH v2 3/8] VM_LOCKED check don't need pte lock

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Date:	Thu, 10 Dec 2009 16:31:21 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>
Subject: [RFC][PATCH v2  3/8] VM_LOCKED check don't need pte lock

Currently, page_referenced_one() check VM_LOCKED after taking ptelock.
But it's unnecessary. We can check VM_LOCKED before to take lock.

This patch does it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Reviewed-by: Rik van Riel <riel@...hat.com>
---
 mm/rmap.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 1b50425..fb0983a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -383,21 +383,21 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 	spinlock_t *ptl;
 	int referenced = 0;
 
-	pte = page_check_address(page, mm, address, &ptl, 0);
-	if (!pte)
-		goto out;
-
 	/*
 	 * Don't want to elevate referenced for mlocked page that gets this far,
 	 * in order that it progresses to try_to_unmap and is moved to the
 	 * unevictable list.
 	 */
 	if (vma->vm_flags & VM_LOCKED) {
-		*mapcount = 1;	/* break early from loop */
+		*mapcount = 0;	/* break early from loop */
 		*vm_flags |= VM_LOCKED;
-		goto out_unmap;
+		goto out;
 	}
 
+	pte = page_check_address(page, mm, address, &ptl, 0);
+	if (!pte)
+		goto out;
+
 	if (ptep_clear_flush_young_notify(vma, address, pte)) {
 		/*
 		 * Don't treat a reference through a sequentially read
@@ -416,7 +416,6 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 			rwsem_is_locked(&mm->mmap_sem))
 		referenced++;
 
-out_unmap:
 	(*mapcount)--;
 	pte_unmap_unlock(pte, ptl);
 
-- 
1.6.5.2



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