Subject: [PATCH] mm: make working set portion that is protected tunable

From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>

In discussion with Rik van Riel and Joannes Weiner we came up that there are
cases that want the current "save 50%" for the working set all the time and
others that would benefit from protectig only a smaller amount.

Eventually no "carved in stone" in kernel ratio will match all use cases,
therefore this patch makes the value tunable via a /proc/sys/vm/ interface
named active_inactive_ratio.

Example configurations might be:
- 50% - like the current kernel
- 0%  - like a kernel pre "56e49d21 vmscan: evict use-once pages first"
- x%  - any other percentage to allow customizing the system to its needs.

Due to our experiments the suggested default in this patch is 25%, but if
preferred I'm fine keeping 50% and letting admins/distros adapt as needed.

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
---

[diffstat]

[diff]
Index: linux-2.6/Documentation/sysctl/vm.txt
===================================================================
--- linux-2.6.orig/Documentation/sysctl/vm.txt	2010-04-21 06:32:23.000000000 +0200
+++ linux-2.6/Documentation/sysctl/vm.txt	2010-04-21 07:24:35.000000000 +0200
@@ -18,6 +18,7 @@
 
 Currently, these files are in /proc/sys/vm:
 
+- active_inactive_ratio
 - block_dump
 - dirty_background_bytes
 - dirty_background_ratio
@@ -57,6 +58,15 @@
 
 ==============================================================
 
+active_inactive_ratio
+
+The kernel tries to protect the active working set. Therefore a portion of the
+file pages is protected, meaning they are omitted when eviting pages until this
+ratio is reached.
+This tunable represents that ratio in percent and specifies the protected part
+
+==============================================================
+
 block_dump
 
 block_dump enables block I/O debugging when set to a nonzero value. More
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c	2010-04-21 06:33:43.000000000 +0200
+++ linux-2.6/kernel/sysctl.c	2010-04-21 07:26:35.000000000 +0200
@@ -1271,6 +1271,15 @@
 		.extra2		= &one,
 	},
 #endif
+	{
+		.procname	= "active_inactive_ratio",
+		.data		= &sysctl_active_inactive_ratio,
+		.maxlen		= sizeof(sysctl_active_inactive_ratio),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one_hundred,
+	},
 
 /*
  * NOTE: do not add new entries to this table unless you have read
Index: linux-2.6/mm/memcontrol.c
===================================================================
--- linux-2.6.orig/mm/memcontrol.c	2010-04-21 06:31:29.000000000 +0200
+++ linux-2.6/mm/memcontrol.c	2010-04-21 09:00:22.000000000 +0200
@@ -893,12 +893,12 @@
 int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
 {
 	unsigned long active;
-	unsigned long inactive;
+	unsigned long file;
 
-	inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
 	active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
+	file = active + mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
 
-	return (active > inactive);
+	return (active > file * sysctl_active_inactive_ratio / 100);
 }
 
 unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c	2010-04-21 06:31:29.000000000 +0200
+++ linux-2.6/mm/vmscan.c	2010-04-21 09:00:13.000000000 +0200
@@ -1459,14 +1459,23 @@
 	return low;
 }
 
+/*
+ * sysctl_active_inactive_ratio
+ *
+ * Defines the portion of file pages within the active working set is going to
+ * be protected. The value represents the percentage that will be protected.
+ */
+int sysctl_active_inactive_ratio __read_mostly = 25;
+
 static int inactive_file_is_low_global(struct zone *zone)
 {
-	unsigned long active, inactive;
+	unsigned long active, file;
 
 	active = zone_page_state(zone, NR_ACTIVE_FILE);
-	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
+	file = active + zone_page_state(zone, NR_INACTIVE_FILE);
+
+	return (active > file * sysctl_active_inactive_ratio / 100);
 
-	return (active > inactive);
 }
 
 /**
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h	2010-04-21 09:02:37.000000000 +0200
+++ linux-2.6/include/linux/mm.h	2010-04-21 09:02:51.000000000 +0200
@@ -1467,5 +1467,7 @@
 
 extern void dump_page(struct page *page);
 
+extern int sysctl_active_inactive_ratio;
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */