From: Hans-Joachim Picht <hpicht@redhat.com>
Date: Fri, 28 Aug 2009 14:00:27 -0400
Subject: [s390] optimize storage key operations for anon pages
Message-id: <20090828140027.GC7396@blc4eb509856389.ibm.com>
Patchwork-id: 20813
O-Subject: [RHEL5 U5 PATCH 1/1] s390 - kernel: Optimize storage key
	operations for anon pages
Bugzilla: 519977
RH-Acked-by: Dean Nelson <dnelson@redhat.com>
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>
RH-Acked-by: Larry Woodman <lwoodman@redhat.com>

Description
============

For anonymous pages without a swap cache backing the check in
page_remove_rmap() for the physical dirty bit is unnecessary.
The instructions that are used to check and reset the dirty bit
are expensive.
This results in poor performance when anoynmous mappings are removed.

The solution is to remove the check for anonymous pages that aren't
swap cache backed.


Bugzilla
=========

BZ 519977
https://bugzilla.redhat.com/show_bug.cgi?id=519977

Upstream status of the patch:
=============================

The patch is upstream as of kernel version 2.6.27

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=a4b526b3ba6353cd89a38e41da48ed83b0ead16f

Test status:
============

The patch has been tested and fixes the problem.
The fix has been verified by the IBM test department.

Please ACK.

With best regards,

	--Hans



diff --git a/mm/rmap.c b/mm/rmap.c
index 3c53315..da83d7b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -495,10 +495,11 @@ int page_mkclean(struct page *page)
 
 	if (page_mapped(page)) {
 		struct address_space *mapping = page_mapping(page);
-		if (mapping)
+		if (mapping) {
 			ret = page_mkclean_file(mapping, page);
-		if (page_test_and_clear_dirty(page))
-			ret = 1;
+			if (page_test_and_clear_dirty(page))
+				ret = 1;
+		}
 	}
 
 	return ret;
@@ -597,7 +598,8 @@ void page_remove_rmap(struct page *page)
 		 * Leaving it set also helps swapoff to reinstate ptes
 		 * faster for those pages still in swapcache.
 		 */
-		if (page_test_and_clear_dirty(page))
+		if ((!PageAnon(page) || PageSwapCache(page)) &&
+		    page_test_and_clear_dirty(page))
 			set_page_dirty(page);
 		__dec_zone_page_state(page,
 				PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);