linux-kernel - [PATCH] don't waste swap on locked pages

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Date:	Wed, 28 Nov 2007 18:59:57 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Ethan Solomita <solo@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] don't waste swap on locked pages

try_to_unmap always fails on a page found in a VM_LOCKED vma (unless
migrating), and recycles it back to the active list.  But if it's an
anonymous page, we've already allocated swap to it: just wasting swap.
Spot locked pages in page_referenced_one and treat them as referenced.

Signed-off-by: Hugh Dickins <hugh@...itas.com>
Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---

 mm/rmap.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 2.6.24-rc3-git/mm/rmap.c	2007-11-27 05:00:22.000000000 +0000
+++ linux/mm/rmap.c	2007-11-28 17:01:20.000000000 +0000
@@ -284,7 +284,10 @@ static int page_referenced_one(struct pa
 	if (!pte)
 		goto out;
 
-	if (ptep_clear_flush_young(vma, address, pte))
+	if (vma->vm_flags & VM_LOCKED) {
+		referenced++;
+		*mapcount = 1;	/* break early from loop */
+	} else if (ptep_clear_flush_young(vma, address, pte))
 		referenced++;
 
 	/* Pretend the page is referenced if the task has the
-
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