[Devel] [RFC][ only for review ] memory controller bacground reclaim [4/5] high/low watermark for memory controller

[KAMEZAWA Hiroyuki]

High Low watermark for page reclaiming in memory cgroup(1)

High-Low value here is implemented for support background reclaim.

 - If USAGE is bigger than high watermark, background reclaim starts.
 - If USAGE is lower than low watermark, background reclaim stops.

Each value is represented in bytes.
(Not configurable now, but can be easily.)
The routine which reclaim is in the next patch. This patch just adds
high/low watermark value.

Changes from YAMAMOTO-san's version
  - I like automatic adjustment of high/low watermark.
    So, I added a code to modify high/low watermark every time the limit
    changes. A user can custorimize it by hand later.
    (I think 93%/97% is not so bad value. need investigation.)

TODO:
 - update documentation.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

 mm/memcontrol.c |   63 ++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 6 deletions(-)

Index: linux-2.6.24-rc3-mm1/mm/memcontrol.c
===================================================================
--- linux-2.6.24-rc3-mm1.orig/mm/memcontrol.c	2007-11-28 16:30:44.000000000 +0900
+++ linux-2.6.24-rc3-mm1/mm/memcontrol.c	2007-11-28 16:44:57.000000000 +0900
@@ -108,16 +108,12 @@
 	struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
 };
 
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
  * statistics based on the statistics developed by Rik Van Riel for clock-pro,
  * to help the administrator determine what knobs to tune.
- *
- * TODO: Add a water mark for the memory controller. Reclaim will begin when
- * we hit the water mark. May be even add a low water mark, such that
- * no reclaim occurs from a cgroup at it's low water mark, this is
- * a feature that will be implemented much later in the future.
  */
 struct mem_cgroup {
 	struct cgroup_subsys_state css;
@@ -162,6 +158,15 @@
 #define PAGE_CGROUP_FLAG_CACHE	(0x1)	/* charged as cache */
 #define PAGE_CGROUP_FLAG_ACTIVE (0x2)	/* page is active in this cgroup */
 
+/*
+ * Default value for high-low watermark for start/stop background reclaim.
+ * represented in percent here. can be customized by user later.
+ * This is applied always limit change.
+ */
+#define DEFAULT_WATERMARK_PERCENT_LOW	(93ULL)
+#define DEFAULT_WATERMARK_PERCENT_HIGH	(97ULL)
+
+
 static inline int page_cgroup_nid(struct page_cgroup *pc)
 {
 	return page_to_nid(pc->page);
@@ -926,6 +931,29 @@
 	return 0;
 }
 
+static void mem_cgroup_init_watermark(struct cgroup *cont)
+{
+	struct mem_cgroup *mem;
+	unsigned long long val, high, low;
+	unsigned long flags;
+
+	mem = mem_cgroup_from_cont(cont);
+	spin_lock_irqsave(&mem->res.lock, flags);
+	val = res_counter_get(&mem->res, RES_LIMIT);
+	if (val == (unsigned long long) LLONG_MAX) {
+		low = (unsigned long long) LLONG_MAX;
+		high = (unsigned long long) LLONG_MAX;
+	} else {
+		low = val * DEFAULT_WATERMARK_PERCENT_LOW / 100ULL;
+		high = val * DEFAULT_WATERMARK_PERCENT_HIGH / 100ULL;
+	}
+	res_counter_set(&mem->res, RES_LOW_WATERMARK, low);
+	res_counter_set(&mem->res, RES_HIGH_WATERMARK, high);
+	spin_unlock_irqrestore(&mem->res.lock, flags);
+	return;
+}
+
+
 static ssize_t mem_cgroup_read(struct cgroup *cont,
 			struct cftype *cft, struct file *file,
 			char __user *userbuf, size_t nbytes, loff_t *ppos)
@@ -944,6 +972,17 @@
 				mem_cgroup_write_strategy);
 }
 
+static ssize_t mem_cgroup_write_limit(struct cgroup *cont, struct cftype *cft,
+				struct file *file, const char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	ssize_t ret;
+	ret = mem_cgroup_write(cont, cft, file, userbuf, nbytes, ppos);
+	if (ret > 0)
+		mem_cgroup_init_watermark(cont);
+	return ret;
+}
+
 static ssize_t mem_control_type_write(struct cgroup *cont,
 			struct cftype *cft, struct file *file,
 			const char __user *userbuf,
@@ -1088,7 +1127,7 @@
 	{
 		.name = "limit_in_bytes",
 		.private = RES_LIMIT,
-		.write = mem_cgroup_write,
+		.write = mem_cgroup_write_limit,
 		.read = mem_cgroup_read,
 	},
 	{
@@ -1102,6 +1141,18 @@
 		.read = mem_control_type_read,
 	},
 	{
+		.name = "low_watermark_in_bytes",
+		.private = RES_LOW_WATERMARK,
+		.write = mem_cgroup_write,
+		.read = mem_cgroup_read,
+	},
+	{
+		.name = "high_watermark_in_bytes",
+		.private = RES_HIGH_WATERMARK,
+		.write = mem_cgroup_write,
+		.read = mem_cgroup_read,
+	},
+	{
 		.name = "force_empty",
 		.write = mem_force_empty_write,
 		.read = mem_force_empty_read,

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