> Using numbers like 128 make the code unreadable. I prefer something
> like MEM_CGROUP_BATCH_COUNT since its more readable than 128. If we ever
> propagate batch_count to other dependent functions, I'd much rather do
> it with a well defined name.

here's a new version.

changes from the previous:
- define a constant.  (MEM_CGROUP_BG_RECLAIM_BATCH_COUNT)
  no functional changes.
- don't increment ALLOCSTALL vm event for mem cgroup because
  it isn't appropriate esp. for background reclamation.
  introduce MEM_CGROUP_STAT_ALLOCSTALL instead.
  (its value is same as memory.failcnt unless GFP_ATOMIC.)

YAMAMOTO Takashi


Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
---

--- linux-2.6.24-rc2-mm1-kame-pd/include/linux/res_counter.h.BACKUP	2007-11-14 16:05:48.000000000 +0900
+++ linux-2.6.24-rc2-mm1-kame-pd/include/linux/res_counter.h	2007-11-22 15:14:32.000000000 +0900
@@ -32,6 +32,13 @@ struct res_counter {
 	 * the number of unsuccessful attempts to consume the resource
 	 */
 	unsigned long long failcnt;
+
+	/*
+	 * watermarks
+	 */
+	unsigned long long high_watermark;
+	unsigned long long low_watermark;
+
 	/*
 	 * the lock to protect all of the above.
 	 * the routines below consider this to be IRQ-safe
@@ -66,6 +73,8 @@ enum {
 	RES_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
+	RES_HIGH_WATERMARK,
+	RES_LOW_WATERMARK,
 };
 
 /*
@@ -124,4 +133,26 @@ static inline bool res_counter_check_und
 	return ret;
 }
 
+static inline bool res_counter_below_low_watermark(struct res_counter *cnt)
+{
+	bool ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cnt->lock, flags);
+	ret = cnt->usage < cnt->low_watermark;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+	return ret;
+}
+
+static inline bool res_counter_above_high_watermark(struct res_counter *cnt)
+{
+	bool ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cnt->lock, flags);
+	ret = cnt->usage > cnt->high_watermark;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+	return ret;
+}
+
 #endif
--- linux-2.6.24-rc2-mm1-kame-pd/kernel/res_counter.c.BACKUP	2007-11-14 16:05:52.000000000 +0900
+++ linux-2.6.24-rc2-mm1-kame-pd/kernel/res_counter.c	2007-11-22 15:14:32.000000000 +0900
@@ -17,6 +17,8 @@ void res_counter_init(struct res_counter
 {
 	spin_lock_init(&counter->lock);
 	counter->limit = (unsigned long long)LLONG_MAX;
+	counter->high_watermark = (unsigned long long)LLONG_MAX;
+	counter->low_watermark = (unsigned long long)LLONG_MAX;
 }
 
 int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
@@ -69,6 +71,10 @@ res_counter_member(struct res_counter *c
 		return &counter->limit;
 	case RES_FAILCNT:
 		return &counter->failcnt;
+	case RES_HIGH_WATERMARK:
+		return &counter->high_watermark;
+	case RES_LOW_WATERMARK:
+		return &counter->low_watermark;
 	};
 
 	BUG();
@@ -99,6 +105,7 @@ ssize_t res_counter_write(struct res_cou
 	int ret;
 	char *buf, *end;
 	unsigned long long tmp, *val;
+	unsigned long flags;
 
 	buf = kmalloc(nbytes + 1, GFP_KERNEL);
 	ret = -ENOMEM;
@@ -122,9 +129,29 @@ ssize_t res_counter_write(struct res_cou
 			goto out_free;
 	}
 
+	spin_lock_irqsave(&counter->lock, flags);
 	val = res_counter_member(counter, member);
+	/* ensure low_watermark <= high_watermark <= limit */
+	switch (member) {
+	case RES_LIMIT:
+		if (tmp < counter->high_watermark)
+			goto out_locked;
+		break;
+	case RES_HIGH_WATERMARK:
+		if (tmp > counter->limit || tmp < counter->low_watermark)
+			goto out_locked;
+		break;
+	case RES_LOW_WATERMARK:
+		if (tmp > counter->high_watermark)
+			goto out_locked;
+		break;
+	}
 	*val = tmp;
+	BUG_ON(counter->high_watermark > counter->limit);
+	BUG_ON(counter->low_watermark > counter->high_watermark);
 	ret = nbytes;
+out_locked:
+	spin_unlock_irqrestore(&counter->lock, flags);
 out_free:
 	kfree(buf);
 out:
--- linux-2.6.24-rc2-mm1-kame-pd/mm/vmscan.c.BACKUP	2007-11-20 13:11:09.000000000 +0900
+++ linux-2.6.24-rc2-mm1-kame-pd/mm/vmscan.c	2007-11-27 08:09:51.000000000 +0900
@@ -1333,7 +1333,6 @@ static unsigned long do_try_to_free_page
 	unsigned long lru_pages = 0;
 	int i;
 
-	count_vm_event(ALLOCSTALL);
 	/*
 	 * mem_cgroup will not do shrink_slab.
 	 */
@@ -1432,6 +1431,7 @@ unsigned long try_to_free_pages(struct z
 		.isolate_pages = isolate_pages_global,
 	};
 
+	count_vm_event(ALLOCSTALL);
 	return do_try_to_free_pages(zones, gfp_mask, &sc);
 }
 
--- linux-2.6.24-rc2-mm1-kame-pd/mm/memcontrol.c.BACKUP	2007-11-20 13:11:09.000000000 +0900
+++ linux-2.6.24-rc2-mm1-kame-pd/mm/memcontrol.c	2007-11-27 08:27:10.000000000 +0900
@@ -28,6 +28,7 @@
 #include <linux/rcupdate.h>
 #include <linux/swap.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
 #include <linux/fs.h>
 #include <linux/seq_file.h>
 
@@ -35,6 +36,7 @@
 
 struct cgroup_subsys mem_cgroup_subsys;
 static const int MEM_CGROUP_RECLAIM_RETRIES = 5;
+static const int MEM_CGROUP_BG_RECLAIM_BATCH_COUNT = 128; /* XXX arbitrary */
 
 /*
  * Statistics for memory cgroup.
@@ -45,6 +47,7 @@ enum mem_cgroup_stat_index {
 	 */
 	MEM_CGROUP_STAT_CACHE, 	   /* # of pages charged as cache */
 	MEM_CGROUP_STAT_RSS,	   /* # of pages charged as rss */
+	MEM_CGROUP_STAT_ALLOCSTALL,/* allocation stalled due to memory.limit */
 
 	MEM_CGROUP_STAT_NSTATS,
 };
@@ -138,6 +141,10 @@ struct mem_cgroup {
 	 * statistics.
 	 */
 	struct mem_cgroup_stat stat;
+	/*
+	 * background reclamation.
+	 */
+	struct work_struct reclaim_work;
 };
 
 /*
@@ -240,6 +247,21 @@ static unsigned long mem_cgroup_get_all_
 
 static struct mem_cgroup init_mem_cgroup;
 
+static DEFINE_MUTEX(mem_cgroup_workqueue_init_lock);
+static struct workqueue_struct *mem_cgroup_workqueue;
+
+static void mem_cgroup_create_workqueue(void)
+{
+
+	if (mem_cgroup_workqueue != NULL)
+		return;
+
+	mutex_lock(&mem_cgroup_workqueue_init_lock);
+	if (mem_cgroup_workqueue == NULL)
+		mem_cgroup_workqueue = create_workqueue("mem_cgroup");
+	mutex_unlock(&mem_cgroup_workqueue_init_lock);
+}
+
 static inline
 struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
 {
@@ -566,6 +588,45 @@ unsigned long mem_cgroup_isolate_pages(u
 	return nr_taken;
 }
 
+static void
+mem_cgroup_schedule_reclaim(struct mem_cgroup *mem)
+{
+
+	if (mem_cgroup_workqueue == NULL) {
+		BUG_ON(mem->css.cgroup->parent != NULL);
+		return;
+	}
+
+	if (work_pending(&mem->reclaim_work))
+		return;
+
+	css_get(&mem->css); /* XXX need some thoughts wrt cgroup removal. */
+	/*
+	 * XXX workqueue is not an ideal mechanism for our purpose.
+	 * revisit later.
+	 */
+	if (!queue_work(mem_cgroup_workqueue, &mem->reclaim_work))
+		css_put(&mem->css);
+}
+
+static void
+mem_cgroup_reclaim(struct work_struct *work)
+{
+	struct mem_cgroup * const mem =
+	    container_of(work, struct mem_cgroup, reclaim_work);
+	int batch_count = MEM_CGROUP_BG_RECLAIM_BATCH_COUNT;
+
+	for (; batch_count > 0; batch_count--) {
+		if (res_counter_below_low_watermark(&mem->res))
+			break;
+		if (!try_to_free_mem_cgroup_pages(mem, GFP_KERNEL))
+			break;
+	}
+	if (batch_count == 0)
+		mem_cgroup_schedule_reclaim(mem);
+	css_put(&mem->css);
+}
+
 /*
  * Charge the memory controller for page usage.
  * Return
@@ -631,6 +692,12 @@ retry:
 	rcu_read_unlock();
 
 	/*
+	 * schedule background reclaim if we are above the high watermark.
+	 */
+	if (res_counter_above_high_watermark(&mem->res))
+		mem_cgroup_schedule_reclaim(mem);
+
+	/*
 	 * If we created the page_cgroup, we should free it on exceeding
 	 * the cgroup limit.
 	 */
@@ -642,6 +709,10 @@ retry:
 		if (is_atomic)
 			goto noreclaim;
 
+		preempt_disable();
+		__mem_cgroup_stat_add_safe(&mem->stat,
+		    MEM_CGROUP_STAT_ALLOCSTALL, 1);
+		preempt_enable();
 		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
 			continue;
 
@@ -939,9 +1010,16 @@ static ssize_t mem_cgroup_write(struct c
 				struct file *file, const char __user *userbuf,
 				size_t nbytes, loff_t *ppos)
 {
-	return res_counter_write(&mem_cgroup_from_cont(cont)->res,
+	ssize_t ret;
+
+	ret = res_counter_write(&mem_cgroup_from_cont(cont)->res,
 				cft->private, userbuf, nbytes, ppos,
 				mem_cgroup_write_strategy);
+
+	if (ret >= 0 && cft->private == RES_HIGH_WATERMARK)
+		mem_cgroup_create_workqueue();
+
+	return ret;
 }
 
 static ssize_t mem_control_type_write(struct cgroup *cont,
@@ -1031,6 +1109,7 @@ static const struct mem_cgroup_stat_desc
 } mem_cgroup_stat_desc[] = {
 	[MEM_CGROUP_STAT_CACHE] = { "cache", PAGE_SIZE, },
 	[MEM_CGROUP_STAT_RSS] = { "rss", PAGE_SIZE, },
+	[MEM_CGROUP_STAT_ALLOCSTALL] = { "allocstall", 1, },
 };
 
 static int mem_control_stat_show(struct seq_file *m, void *arg)
@@ -1097,6 +1176,18 @@ static struct cftype mem_cgroup_files[] 
 		.read = mem_cgroup_read,
 	},
 	{
+		.name = "high_watermark_in_bytes",
+		.private = RES_HIGH_WATERMARK,
+		.write = mem_cgroup_write,
+		.read = mem_cgroup_read,
+	},
+	{
+		.name = "low_watermark_in_bytes",
+		.private = RES_LOW_WATERMARK,
+		.write = mem_cgroup_write,
+		.read = mem_cgroup_read,
+	},
+	{
 		.name = "control_type",
 		.write = mem_control_type_write,
 		.read = mem_control_type_read,
@@ -1161,6 +1252,8 @@ mem_cgroup_create(struct cgroup_subsys *
 		if (alloc_mem_cgroup_per_zone_info(mem, node))
 			goto free_out;
 
+	INIT_WORK(&mem->reclaim_work, mem_cgroup_reclaim);
+
 	return &mem->css;
 free_out:
 	for_each_node_state(node, N_POSSIBLE)
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