[RFC] [PATCH] memory controller background reclamation

[YAMAMOTO Takashi]

hi,

i implemented background reclamation for your memory controller and
did a few benchmarks with and without it.  any comments?

YAMAMOTO Takashi


-----
"time make -j4 bzImage" in a cgroup with 64MB limit:

	without patch:
		real    22m22.389s
		user    13m35.163s
		sys     6m12.283s

		memory.failcnt after a run: 106647

	with patch:
		real    19m25.860s
		user    14m10.549s
		sys     6m13.831s

		memory.failcnt after a run: 35366

"for x in 1 2 3;do time dd if=/dev/zero bs=1M count=300|tail;done"
in a cgroup with 16MB limit:

	without patch:
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 19.0058 seconds, 16.6 MB/s
		u 0.00s s 0.67s e 19.01s maj 90 min 2021 in 0 out 0
		u 0.48s s 7.22s e 93.13s maj 20475 min 210903 in 0 out 0
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 14.8394 seconds, 21.2 MB/s
		u 0.00s s 0.63s e 14.84s maj 53 min 1392 in 0 out 0
		u 0.48s s 7.00s e 94.39s maj 20125 min 211145 in 0 out 0
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 14.0635 seconds, 22.4 MB/s
		u 0.01s s 0.59s e 14.07s maj 50 min 1385 in 0 out 0
		u 0.57s s 6.93s e 91.54s maj 20359 min 210911 in 0 out 0

		memory.failcnt after a run: 8804

	with patch:
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 5.94875 seconds, 52.9 MB/s
		u 0.00s s 0.67s e 5.95s maj 206 min 5393 in 0 out 0
		u 0.45s s 6.63s e 46.07s maj 21350 min 210252 in 0 out 0
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 8.16441 seconds, 38.5 MB/s
		u 0.00s s 0.60s e 8.17s maj 240 min 4614 in 0 out 0
		u 0.45s s 6.56s e 54.56s maj 22298 min 209255 in 0 out 0
		300+0 records in
		300+0 records out
		314572800 bytes (315 MB) copied, 4.60967 seconds, 68.2 MB/s
		u 0.00s s 0.60s e 4.64s maj 196 min 4733 in 0 out 0
		u 0.46s s 6.53s e 49.28s maj 22223 min 209384 in 0 out 0

		memory.failcnt after a run: 1589
-----


--- linux-2.6.23-rc8-mm2-cgkswapd/mm/memcontrol.c.BACKUP	2007-10-01 17:19:57.000000000 +0900
+++ linux-2.6.23-rc8-mm2-cgkswapd/mm/memcontrol.c	2007-10-22 13:46:01.000000000 +0900
@@ -27,6 +27,7 @@
 #include <linux/rcupdate.h>
 #include <linux/swap.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
 #include <linux/fs.h>
 
 #include <asm/uaccess.h>
@@ -63,6 +64,8 @@ struct mem_cgroup {
 	 */
 	spinlock_t lru_lock;
 	unsigned long control_type;	/* control RSS or RSS+Pagecache */
+
+	struct work_struct reclaim_work;
 };
 
 /*
@@ -95,6 +98,9 @@ enum {
 
 static struct mem_cgroup init_mem_cgroup;
 
+static DEFINE_MUTEX(mem_cgroup_workqueue_init_lock);
+static struct workqueue_struct *mem_cgroup_workqueue;
+
 static inline
 struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
 {
@@ -250,6 +256,69 @@ unsigned long mem_cgroup_isolate_pages(u
 	return nr_taken;
 }
 
+static int
+mem_cgroup_need_reclaim(struct mem_cgroup *mem)
+{
+	struct res_counter * const cnt = &mem->res;
+	int doreclaim;
+	unsigned long flags;
+
+	/* XXX should be in res_counter */
+	/* XXX should not hardcode a watermark */
+	spin_lock_irqsave(&cnt->lock, flags);
+	doreclaim = cnt->usage > cnt->limit / 4 * 3;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+
+	return doreclaim;
+}
+
+static void
+mem_cgroup_schedule_reclaim_if_necessary(struct mem_cgroup *mem)
+{
+
+	if (mem_cgroup_workqueue == NULL) {
+		BUG_ON(mem->css.cgroup->parent != NULL);
+		return;
+	}
+
+	if (work_pending(&mem->reclaim_work))
+		return;
+
+	if (!mem_cgroup_need_reclaim(mem))
+		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 = 128; /* XXX arbitrary */
+
+	for (; batch_count > 0; batch_count--) {
+		if (!mem_cgroup_need_reclaim(mem))
+			break;
+		/*
+		 * XXX try_to_free_foo is not a correct mechanism to
+		 * use here.  eg. ALLOCSTALL counter
+		 * revisit later.
+		 */
+		if (!try_to_free_mem_cgroup_pages(mem, GFP_KERNEL))
+			break;
+	}
+	if (batch_count == 0)
+		mem_cgroup_schedule_reclaim_if_necessary(mem);
+	css_put(&mem->css);
+}
+
 /*
  * Charge the memory controller for page usage.
  * Return
@@ -311,6 +380,9 @@ int mem_cgroup_charge(struct page *page,
 	 */
 	while (res_counter_charge(&mem->res, PAGE_SIZE)) {
 		bool is_atomic = gfp_mask & GFP_ATOMIC;
+
+		mem_cgroup_schedule_reclaim_if_necessary(mem);
+
 		/*
 		 * We cannot reclaim under GFP_ATOMIC, fail the charge
 		 */
@@ -551,8 +623,18 @@ mem_cgroup_create(struct cgroup_subsys *
 	if (unlikely((cont->parent) == NULL)) {
 		mem = &init_mem_cgroup;
 		init_mm.mem_cgroup = mem;
-	} else
+	} else {
+		/* XXX too late for the top-level cgroup */
+		if (mem_cgroup_workqueue == NULL) {
+			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);
+		}
 		mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
+	}
 
 	if (mem == NULL)
 		return NULL;
@@ -562,6 +644,7 @@ mem_cgroup_create(struct cgroup_subsys *
 	INIT_LIST_HEAD(&mem->inactive_list);
 	spin_lock_init(&mem->lru_lock);
 	mem->control_type = MEM_CGROUP_TYPE_ALL;
+	INIT_WORK(&mem->reclaim_work, mem_cgroup_reclaim);
 	return &mem->css;
 }