From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Sun, 24 Jul 2011 08:47:59 +0000 (+0200)
Subject: [S390] reference bit testing for unmapped pages
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=50a15981a1fac7e019ff7c3cba87531fb580f065;p=mv-sheeva.git

[S390] reference bit testing for unmapped pages

On x86 a page without a mapper is by definition not referenced / old.
The s390 architecture keeps the reference bit in the storage key and
the current code will check the storage key for page without a mapper.
This leads to an interesting effect: the first time an s390 system
needs to write pages to swap it only finds referenced pages. This
causes a lot of pages to get added and written to the swap device.
To avoid this behaviour change page_referenced to query the storage
key only if there is a mapper of the page.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

diff --git a/mm/rmap.c b/mm/rmap.c
index 2540a39eea4..9701574bb67 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -869,11 +869,11 @@ int page_referenced(struct page *page,
 								vm_flags);
 		if (we_locked)
 			unlock_page(page);
+
+		if (page_test_and_clear_young(page_to_pfn(page)))
+			referenced++;
 	}
 out:
-	if (page_test_and_clear_young(page_to_pfn(page)))
-		referenced++;
-
 	return referenced;
 }