hi,

here's a patch to implement memory.min_usage,
which controls the minimum memory usage for a cgroup.

it works similarly to mlock;
global memory reclamation doesn't reclaim memory from
cgroups whose memory usage is below the value.
setting it too high is a dangerous operation.

it's against 2.6.24-rc3-mm2 + memory.swappiness patch i posted here yesterday.
but it's logically independent from the swappiness patch.

todo:
- restrict non-root user's operation ragardless of owner of cgroupfs files?
- make oom killer aware of this?

YAMAMOTO Takashi


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

--- linux-2.6.24-rc3-mm2-swappiness/include/linux/memcontrol.h.BACKUP2	2007-12-03 13:52:37.000000000 +0900
+++ linux-2.6.24-rc3-mm2-swappiness/include/linux/memcontrol.h	2007-12-03 14:07:45.000000000 +0900
@@ -47,6 +47,7 @@ extern int mem_cgroup_cache_charge(struc
 					gfp_t gfp_mask);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 extern int mem_cgroup_swappiness(struct mem_cgroup *mem);
+extern int mem_cgroup_canreclaim(struct page *page, struct mem_cgroup *mem);
 
 static inline struct mem_cgroup *mm_cgroup(const struct mm_struct *mm)
 {
--- linux-2.6.24-rc3-mm2-swappiness/mm/memcontrol.c.BACKUP2	2007-12-03 13:52:13.000000000 +0900
+++ linux-2.6.24-rc3-mm2-swappiness/mm/memcontrol.c	2007-12-04 11:42:07.000000000 +0900
@@ -134,6 +134,7 @@ struct mem_cgroup {
 	unsigned long control_type;	/* control RSS or RSS+Pagecache */
 	int	prev_priority;	/* for recording reclaim priority */
 	unsigned int swappiness;	/* swappiness */
+	unsigned long long min_usage; /* XXX should be a part of res_counter? */
 	/*
 	 * statistics.
 	 */
@@ -1096,6 +1097,22 @@ static u64 mem_cgroup_swappiness_read(st
 	return mem->swappiness;
 }
 
+static int mem_cgroup_min_usage_write(struct cgroup *cont, struct cftype *cft,
+				       u64 val)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
+
+	mem->min_usage = val;
+	return 0;
+}
+
+static u64 mem_cgroup_min_usage_read(struct cgroup *cont, struct cftype *cft)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
+
+	return mem->min_usage;
+}
+
 static struct cftype mem_cgroup_files[] = {
 	{
 		.name = "usage_in_bytes",
@@ -1132,6 +1149,11 @@ static struct cftype mem_cgroup_files[] 
 		.write_uint = mem_cgroup_swappiness_write,
 		.read_uint = mem_cgroup_swappiness_read,
 	},
+	{
+		.name = "min_usage_in_bytes",
+		.write_uint = mem_cgroup_min_usage_write,
+		.read_uint = mem_cgroup_min_usage_read,
+	},
 };
 
 /* XXX probably it's better to move try_to_free_mem_cgroup_pages to
@@ -1142,6 +1164,36 @@ int mem_cgroup_swappiness(struct mem_cgr
 	return mem->swappiness;
 }
 
+int mem_cgroup_canreclaim(struct page *page, struct mem_cgroup *mem1)
+{
+	struct page_cgroup *pc;
+	int result = 1;
+
+	if (mem1 != NULL)
+		return 1;
+
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc) {
+		struct mem_cgroup *mem2 = pc->mem_cgroup;
+		unsigned long long min_usage;
+
+		BUG_ON(mem2 == NULL);
+		min_usage = mem2->min_usage;
+		if (min_usage != 0) {
+			unsigned long flags;
+
+			spin_lock_irqsave(&mem2->res.lock, flags);
+			if (mem2->res.usage <= min_usage)
+				result = 0;
+			spin_unlock_irqrestore(&mem2->res.lock, flags);
+		}
+	}
+	unlock_page_cgroup(page);
+
+	return result;
+}
+
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
 {
 	struct mem_cgroup_per_node *pn;
--- linux-2.6.24-rc3-mm2-swappiness/mm/vmscan.c.BACKUP2	2007-12-03 13:52:22.000000000 +0900
+++ linux-2.6.24-rc3-mm2-swappiness/mm/vmscan.c	2007-12-03 14:11:42.000000000 +0900
@@ -531,6 +531,11 @@ static unsigned long shrink_page_list(st
 					referenced && page_mapping_inuse(page))
 			goto activate_locked;
 
+#ifdef CONFIG_CGROUP_MEM_CONT
+		if (!mem_cgroup_canreclaim(page, sc->mem_cgroup))
+			goto activate_locked;
+#endif /* CONFIG_CGROUP_MEM_CONT */
+
 #ifdef CONFIG_SWAP
 		/*
 		 * Anonymous process memory has backing store?
@@ -1122,6 +1127,12 @@ static void shrink_active_list(unsigned 
 			list_add(&page->lru, &l_active);
 			continue;
 		}
+#ifdef CONFIG_CGROUP_MEM_CONT
+		if (!mem_cgroup_canreclaim(page, sc->mem_cgroup)) {
+			list_add(&page->lru, &l_active);
+			continue;
+		}
+#endif /* CONFIG_CGROUP_MEM_CONT */
 		list_add(&page->lru, &l_inactive);
 	}
 
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