[PATCH][for -mm] Fix and Enhancements for memory cgroup [6/6] add force reclaim interface

[KAMEZAWA Hiroyuki]

This patch adds an interface "memory.force_reclaim".
Any write to this file will drop all charges in this cgroup if
there is no task under.

%echo 1 > /....../memory.force_reclaim

will drop all charges of memory cgroup if cgroup's tasks is empty.

This is useful to invoke rmdir() against memory cgroup successfully.

Tested and worked well on x86_64/fake-NUMA system.

Changelog:
  - added a new interface force_relcaim.
  - changes spin_lock to spin_lock_irqsave().


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


 mm/memcontrol.c |   79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -507,6 +507,55 @@ retry:
 	return;
 }
 
+static void
+mem_cgroup_force_reclaim_list(struct mem_cgroup *mem, struct list_head *list)
+{
+	struct page_cgroup *pc;
+	struct page *page;
+	int count = SWAP_CLUSTER_MAX;
+	unsigned long flags;
+
+	spin_lock_irqsave(&mem->lru_lock, flags);
+
+	while (!list_empty(list)) {
+		pc = list_entry(list->prev, struct page_cgroup, lru);
+		page = pc->page;
+		if (clear_page_cgroup(page, pc) == pc) {
+			css_put(&mem->css);
+			res_counter_uncharge(&mem->res, PAGE_SIZE);
+			list_del_init(&pc->lru);
+			kfree(pc);
+		} else
+			count = 1; /* race? ...do relax */
+
+		if (--count == 0) {
+			spin_unlock_irqrestore(&mem->lru_lock, flags);
+			cond_resched();
+			spin_lock_irqsave(&mem->lru_lock, flags);
+			count = SWAP_CLUSTER_MAX;
+		}
+	}
+	spin_unlock_irqrestore(&mem->lru_lock, flags);
+}
+
+int mem_cgroup_force_reclaim(struct mem_cgroup *mem)
+{
+	int ret = -EBUSY;
+	while (!list_empty(&mem->active_list) ||
+	       !list_empty(&mem->inactive_list)) {
+		if (atomic_read(&mem->css.cgroup->count) > 0)
+			goto out;
+		mem_cgroup_force_reclaim_list(mem, &mem->active_list);
+		mem_cgroup_force_reclaim_list(mem, &mem->inactive_list);
+	}
+	ret = 0;
+out:
+	css_put(&mem->css);
+	return ret;
+}
+
+
+
 int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
 {
 	*tmp = memparse(buf, &buf);
@@ -592,6 +641,31 @@ static ssize_t mem_control_type_read(str
 			ppos, buf, s - buf);
 }
 
+
+static ssize_t mem_force_reclaim_write(struct cgroup *cont,
+				struct cftype *cft, struct file *file,
+				const char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
+	int ret;
+	ret = mem_cgroup_force_reclaim(mem);
+	if (!ret)
+		ret = nbytes;
+	return ret;
+}
+
+static ssize_t mem_force_reclaim_read(struct cgroup *cont,
+				struct cftype *cft,
+				struct file *file, char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	char buf[2] = "0";
+	return simple_read_from_buffer((void __user *)userbuf, nbytes,
+			ppos, buf, strlen(buf));
+}
+
+
 static struct cftype mem_cgroup_files[] = {
 	{
 		.name = "usage_in_bytes",
@@ -614,6 +688,11 @@ static struct cftype mem_cgroup_files[] 
 		.write = mem_control_type_write,
 		.read = mem_control_type_read,
 	},
+	{
+		.name = "force_reclaim",
+		.write = mem_force_reclaim_write,
+		.read = mem_force_reclaim_read,
+	},
 };
 
 static struct mem_cgroup init_mem_cgroup;