[PATCH V3 1/2] memcg: softlimit reclaim rework

* [PATCH V3 1/2] memcg: softlimit reclaim rework
@ 2012-04-17 16:38 Ying Han
  2012-04-20  9:17 ` Michal Hocko
  0 siblings, 1 reply; 6+ messages in thread
From: Ying Han @ 2012-04-17 16:38 UTC (permalink / raw)
  To: Michal Hocko, Johannes Weiner, Mel Gorman, KAMEZAWA Hiroyuki,
	Rik van Riel, Hillf Danton, Hugh Dickins, Dan Magenheimer,
	Andrew Morton
  Cc: linux-mm

This patch reverts all the existing softlimit reclaim implementations and
instead integrates the softlimit reclaim into existing global reclaim logic.

The new softlimit reclaim includes the following changes:

1. add function should_reclaim_mem_cgroup()

Add the filter function should_reclaim_mem_cgroup() under the common function
shrink_zone(). The later one is being called both from per-memcg reclaim as
well as global reclaim.

Today the softlimit takes effect only under global memory pressure. The memcgs
get free run above their softlimit until there is a global memory contention.
This patch doesn't change the semantics.

Under the global reclaim, we skip reclaiming from a memcg under its softlimit.
To prevent reclaim from trying too hard on hitting memcgs (above softlimit) w/
only hard-to-reclaim pages, the reclaim proirity is used to skip the softlimit
check. This is a trade-off of system performance and resource isolation.

2. detect no memcgs above softlimit under zone reclaim.

The function zone_reclaimable() marks zone->all_unreclaimable based on
per-zone pages_scanned and reclaimable_pages. If all_unreclaimable is true,
alloc_pages could go to OOM instead of getting stuck in page reclaim.

In memcg kernel, cgroup under its softlimit is not targeted under global
reclaim. It could be possible that all memcgs are under their softlimit for
a particular zone. So the direct reclaim do_try_to_free_pages() will always
return 1 which causes the caller __alloc_pages_direct_reclaim() enter tight
loop.

The reclaim priority check we put in should_reclaim_mem_cgroup() should help
this case, but we still don't want to burn cpu cycles for first few priorities
to get to that point. The idea is from LSF discussion where we detect it after
the first round of scanning and restart the reclaim by not looking at softlimit
at all. This allows us to make forward progress on shrink_zone() and free some
pages on the zone.

In order to do the detection for scanning all the memcgs under shrink_zone(),
i have to change the mem_cgroup_iter() from shared walk to full walk. Otherwise,
it would be very easy to skip lots of memcgs above softlimit and it causes the
flag "ignore_softlimit" being mistakenly set.

Signed-off-by: Ying Han <yinghan@google.com>
---
 include/linux/memcontrol.h |   18 +--
 include/linux/swap.h       |    4 -
 mm/memcontrol.c            |  397 +-------------------------------------------
 mm/vmscan.c                |  113 +++++--------
 4 files changed, 55 insertions(+), 477 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f94efd2..b1950af 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -111,6 +111,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
 				   struct mem_cgroup_reclaim_cookie *);
 void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
 
+bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *);
+
 /*
  * For memory reclaim.
  */
@@ -185,9 +187,6 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 	mem_cgroup_update_page_stat(page, idx, -1);
 }
 
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-						gfp_t gfp_mask,
-						unsigned long *total_scanned);
 u64 mem_cgroup_get_limit(struct mem_cgroup *memcg);
 
 void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
@@ -327,6 +326,11 @@ static inline void mem_cgroup_iter_break(struct mem_cgroup *root,
 {
 }
 
+static inline bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *mem)
+{
+	return true;
+}
+
 static inline bool mem_cgroup_disabled(void)
 {
 	return true;
@@ -390,14 +394,6 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 }
 
 static inline
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-					    gfp_t gfp_mask,
-					    unsigned long *total_scanned)
-{
-	return 0;
-}
-
-static inline
 u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
 {
 	return 0;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index b1fd5c7..c9e9279 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -254,10 +254,6 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 extern int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file);
 extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
 						  gfp_t gfp_mask, bool noswap);
-extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
-						gfp_t gfp_mask, bool noswap,
-						struct zone *zone,
-						unsigned long *nr_scanned);
 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 extern int vm_swappiness;
 extern int remove_mapping(struct address_space *mapping, struct page *page);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a7165a6..12be84a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -35,7 +35,6 @@
 #include <linux/limits.h>
 #include <linux/export.h>
 #include <linux/mutex.h>
-#include <linux/rbtree.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
@@ -108,7 +107,6 @@ enum mem_cgroup_events_index {
  */
 enum mem_cgroup_events_target {
 	MEM_CGROUP_TARGET_THRESH,
-	MEM_CGROUP_TARGET_SOFTLIMIT,
 	MEM_CGROUP_TARGET_NUMAINFO,
 	MEM_CGROUP_NTARGETS,
 };
@@ -139,12 +137,6 @@ struct mem_cgroup_per_zone {
 	struct mem_cgroup_reclaim_iter reclaim_iter[DEF_PRIORITY + 1];
 
 	struct zone_reclaim_stat reclaim_stat;
-	struct rb_node		tree_node;	/* RB tree node */
-	unsigned long long	usage_in_excess;/* Set to the value by which */
-						/* the soft limit is exceeded*/
-	bool			on_tree;
-	struct mem_cgroup	*memcg;		/* Back pointer, we cannot */
-						/* use container_of	   */
 };
 
 struct mem_cgroup_per_node {
@@ -155,26 +147,6 @@ struct mem_cgroup_lru_info {
 	struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
 };
 
-/*
- * Cgroups above their limits are maintained in a RB-Tree, independent of
- * their hierarchy representation
- */
-
-struct mem_cgroup_tree_per_zone {
-	struct rb_root rb_root;
-	spinlock_t lock;
-};
-
-struct mem_cgroup_tree_per_node {
-	struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
-};
-
-struct mem_cgroup_tree {
-	struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
-};
-
-static struct mem_cgroup_tree soft_limit_tree __read_mostly;
-
 struct mem_cgroup_threshold {
 	struct eventfd_ctx *eventfd;
 	u64 threshold;
@@ -356,12 +328,7 @@ static bool move_file(void)
 					&mc.to->move_charge_at_immigrate);
 }
 
-/*
- * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
- * limit reclaim to prevent infinite loops, if they ever occur.
- */
 #define	MEM_CGROUP_MAX_RECLAIM_LOOPS		(100)
-#define	MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS	(2)
 
 enum charge_type {
 	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
@@ -394,12 +361,12 @@ enum charge_type {
 static void mem_cgroup_get(struct mem_cgroup *memcg);
 static void mem_cgroup_put(struct mem_cgroup *memcg);
 
+static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
 /* Writing them here to avoid exposing memcg's inner layout */
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
 #include <net/sock.h>
 #include <net/ip.h>
 
-static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
 void sock_update_memcg(struct sock *sk)
 {
 	if (mem_cgroup_sockets_enabled) {
@@ -476,164 +443,6 @@ page_cgroup_zoneinfo(struct mem_cgroup *memcg, struct page *page)
 	return mem_cgroup_zoneinfo(memcg, nid, zid);
 }
 
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_node_zone(int nid, int zid)
-{
-	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_from_page(struct page *page)
-{
-	int nid = page_to_nid(page);
-	int zid = page_zonenum(page);
-
-	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static void
-__mem_cgroup_insert_exceeded(struct mem_cgroup *memcg,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz,
-				unsigned long long new_usage_in_excess)
-{
-	struct rb_node **p = &mctz->rb_root.rb_node;
-	struct rb_node *parent = NULL;
-	struct mem_cgroup_per_zone *mz_node;
-
-	if (mz->on_tree)
-		return;
-
-	mz->usage_in_excess = new_usage_in_excess;
-	if (!mz->usage_in_excess)
-		return;
-	while (*p) {
-		parent = *p;
-		mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
-					tree_node);
-		if (mz->usage_in_excess < mz_node->usage_in_excess)
-			p = &(*p)->rb_left;
-		/*
-		 * We can't avoid mem cgroups that are over their soft
-		 * limit by the same amount
-		 */
-		else if (mz->usage_in_excess >= mz_node->usage_in_excess)
-			p = &(*p)->rb_right;
-	}
-	rb_link_node(&mz->tree_node, parent, p);
-	rb_insert_color(&mz->tree_node, &mctz->rb_root);
-	mz->on_tree = true;
-}
-
-static void
-__mem_cgroup_remove_exceeded(struct mem_cgroup *memcg,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz)
-{
-	if (!mz->on_tree)
-		return;
-	rb_erase(&mz->tree_node, &mctz->rb_root);
-	mz->on_tree = false;
-}
-
-static void
-mem_cgroup_remove_exceeded(struct mem_cgroup *memcg,
-				struct mem_cgroup_per_zone *mz,
-				struct mem_cgroup_tree_per_zone *mctz)
-{
-	spin_lock(&mctz->lock);
-	__mem_cgroup_remove_exceeded(memcg, mz, mctz);
-	spin_unlock(&mctz->lock);
-}
-
-
-static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
-{
-	unsigned long long excess;
-	struct mem_cgroup_per_zone *mz;
-	struct mem_cgroup_tree_per_zone *mctz;
-	int nid = page_to_nid(page);
-	int zid = page_zonenum(page);
-	mctz = soft_limit_tree_from_page(page);
-
-	/*
-	 * Necessary to update all ancestors when hierarchy is used.
-	 * because their event counter is not touched.
-	 */
-	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
-		mz = mem_cgroup_zoneinfo(memcg, nid, zid);
-		excess = res_counter_soft_limit_excess(&memcg->res);
-		/*
-		 * We have to update the tree if mz is on RB-tree or
-		 * mem is over its softlimit.
-		 */
-		if (excess || mz->on_tree) {
-			spin_lock(&mctz->lock);
-			/* if on-tree, remove it */
-			if (mz->on_tree)
-				__mem_cgroup_remove_exceeded(memcg, mz, mctz);
-			/*
-			 * Insert again. mz->usage_in_excess will be updated.
-			 * If excess is 0, no tree ops.
-			 */
-			__mem_cgroup_insert_exceeded(memcg, mz, mctz, excess);
-			spin_unlock(&mctz->lock);
-		}
-	}
-}
-
-static void mem_cgroup_remove_from_trees(struct mem_cgroup *memcg)
-{
-	int node, zone;
-	struct mem_cgroup_per_zone *mz;
-	struct mem_cgroup_tree_per_zone *mctz;
-
-	for_each_node(node) {
-		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-			mz = mem_cgroup_zoneinfo(memcg, node, zone);
-			mctz = soft_limit_tree_node_zone(node, zone);
-			mem_cgroup_remove_exceeded(memcg, mz, mctz);
-		}
-	}
-}
-
-static struct mem_cgroup_per_zone *
-__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
-	struct rb_node *rightmost = NULL;
-	struct mem_cgroup_per_zone *mz;
-
-retry:
-	mz = NULL;
-	rightmost = rb_last(&mctz->rb_root);
-	if (!rightmost)
-		goto done;		/* Nothing to reclaim from */
-
-	mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
-	/*
-	 * Remove the node now but someone else can add it back,
-	 * we will to add it back at the end of reclaim to its correct
-	 * position in the tree.
-	 */
-	__mem_cgroup_remove_exceeded(mz->memcg, mz, mctz);
-	if (!res_counter_soft_limit_excess(&mz->memcg->res) ||
-		!css_tryget(&mz->memcg->css))
-		goto retry;
-done:
-	return mz;
-}
-
-static struct mem_cgroup_per_zone *
-mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
-	struct mem_cgroup_per_zone *mz;
-
-	spin_lock(&mctz->lock);
-	mz = __mem_cgroup_largest_soft_limit_node(mctz);
-	spin_unlock(&mctz->lock);
-	return mz;
-}
-
 /*
  * Implementation Note: reading percpu statistics for memcg.
  *
@@ -778,9 +587,6 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 		case MEM_CGROUP_TARGET_THRESH:
 			next = val + THRESHOLDS_EVENTS_TARGET;
 			break;
-		case MEM_CGROUP_TARGET_SOFTLIMIT:
-			next = val + SOFTLIMIT_EVENTS_TARGET;
-			break;
 		case MEM_CGROUP_TARGET_NUMAINFO:
 			next = val + NUMAINFO_EVENTS_TARGET;
 			break;
@@ -803,11 +609,8 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 	/* threshold event is triggered in finer grain than soft limit */
 	if (unlikely(mem_cgroup_event_ratelimit(memcg,
 						MEM_CGROUP_TARGET_THRESH))) {
-		bool do_softlimit;
 		bool do_numainfo __maybe_unused;
 
-		do_softlimit = mem_cgroup_event_ratelimit(memcg,
-						MEM_CGROUP_TARGET_SOFTLIMIT);
 #if MAX_NUMNODES > 1
 		do_numainfo = mem_cgroup_event_ratelimit(memcg,
 						MEM_CGROUP_TARGET_NUMAINFO);
@@ -815,8 +618,6 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 		preempt_enable();
 
 		mem_cgroup_threshold(memcg);
-		if (unlikely(do_softlimit))
-			mem_cgroup_update_tree(memcg, page);
 #if MAX_NUMNODES > 1
 		if (unlikely(do_numainfo))
 			atomic_inc(&memcg->numainfo_events);
@@ -963,6 +764,14 @@ void mem_cgroup_iter_break(struct mem_cgroup *root,
 		css_put(&prev->css);
 }
 
+bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *mem)
+{
+	if (mem_cgroup_disabled() || mem_cgroup_is_root(mem))
+		return true;
+
+	return res_counter_soft_limit_excess(&mem->res) > 0;
+}
+
 /*
  * Iteration constructs for visiting all cgroups (under a tree).  If
  * loops are exited prematurely (break), mem_cgroup_iter_break() must
@@ -1675,59 +1484,6 @@ bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)
 }
 #endif
 
-static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
-				   struct zone *zone,
-				   gfp_t gfp_mask,
-				   unsigned long *total_scanned)
-{
-	struct mem_cgroup *victim = NULL;
-	int total = 0;
-	int loop = 0;
-	unsigned long excess;
-	unsigned long nr_scanned;
-	struct mem_cgroup_reclaim_cookie reclaim = {
-		.zone = zone,
-		.priority = 0,
-	};
-
-	excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;
-
-	while (1) {
-		victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
-		if (!victim) {
-			loop++;
-			if (loop >= 2) {
-				/*
-				 * If we have not been able to reclaim
-				 * anything, it might because there are
-				 * no reclaimable pages under this hierarchy
-				 */
-				if (!total)
-					break;
-				/*
-				 * We want to do more targeted reclaim.
-				 * excess >> 2 is not to excessive so as to
-				 * reclaim too much, nor too less that we keep
-				 * coming back to reclaim from this cgroup
-				 */
-				if (total >= (excess >> 2) ||
-					(loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
-					break;
-			}
-			continue;
-		}
-		if (!mem_cgroup_reclaimable(victim, false))
-			continue;
-		total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
-						     zone, &nr_scanned);
-		*total_scanned += nr_scanned;
-		if (!res_counter_soft_limit_excess(&root_memcg->res))
-			break;
-	}
-	mem_cgroup_iter_break(root_memcg, victim);
-	return total;
-}
-
 /*
  * Check OOM-Killer is already running under our hierarchy.
  * If someone is running, return false.
@@ -2539,8 +2295,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
 
 	/*
 	 * "charge_statistics" updated event counter. Then, check it.
-	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
-	 * if they exceeds softlimit.
 	 */
 	memcg_check_events(memcg, page);
 }
@@ -3561,98 +3315,6 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
 	return ret;
 }
 
-unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-					    gfp_t gfp_mask,
-					    unsigned long *total_scanned)
-{
-	unsigned long nr_reclaimed = 0;
-	struct mem_cgroup_per_zone *mz, *next_mz = NULL;
-	unsigned long reclaimed;
-	int loop = 0;
-	struct mem_cgroup_tree_per_zone *mctz;
-	unsigned long long excess;
-	unsigned long nr_scanned;
-
-	if (order > 0)
-		return 0;
-
-	mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
-	/*
-	 * This loop can run a while, specially if mem_cgroup's continuously
-	 * keep exceeding their soft limit and putting the system under
-	 * pressure
-	 */
-	do {
-		if (next_mz)
-			mz = next_mz;
-		else
-			mz = mem_cgroup_largest_soft_limit_node(mctz);
-		if (!mz)
-			break;
-
-		nr_scanned = 0;
-		reclaimed = mem_cgroup_soft_reclaim(mz->memcg, zone,
-						    gfp_mask, &nr_scanned);
-		nr_reclaimed += reclaimed;
-		*total_scanned += nr_scanned;
-		spin_lock(&mctz->lock);
-
-		/*
-		 * If we failed to reclaim anything from this memory cgroup
-		 * it is time to move on to the next cgroup
-		 */
-		next_mz = NULL;
-		if (!reclaimed) {
-			do {
-				/*
-				 * Loop until we find yet another one.
-				 *
-				 * By the time we get the soft_limit lock
-				 * again, someone might have aded the
-				 * group back on the RB tree. Iterate to
-				 * make sure we get a different mem.
-				 * mem_cgroup_largest_soft_limit_node returns
-				 * NULL if no other cgroup is present on
-				 * the tree
-				 */
-				next_mz =
-				__mem_cgroup_largest_soft_limit_node(mctz);
-				if (next_mz == mz)
-					css_put(&next_mz->memcg->css);
-				else /* next_mz == NULL or other memcg */
-					break;
-			} while (1);
-		}
-		__mem_cgroup_remove_exceeded(mz->memcg, mz, mctz);
-		excess = res_counter_soft_limit_excess(&mz->memcg->res);
-		/*
-		 * One school of thought says that we should not add
-		 * back the node to the tree if reclaim returns 0.
-		 * But our reclaim could return 0, simply because due
-		 * to priority we are exposing a smaller subset of
-		 * memory to reclaim from. Consider this as a longer
-		 * term TODO.
-		 */
-		/* If excess == 0, no tree ops */
-		__mem_cgroup_insert_exceeded(mz->memcg, mz, mctz, excess);
-		spin_unlock(&mctz->lock);
-		css_put(&mz->memcg->css);
-		loop++;
-		/*
-		 * Could not reclaim anything and there are no more
-		 * mem cgroups to try or we seem to be looping without
-		 * reclaiming anything.
-		 */
-		if (!nr_reclaimed &&
-			(next_mz == NULL ||
-			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
-			break;
-	} while (!nr_reclaimed);
-	if (next_mz)
-		css_put(&next_mz->memcg->css);
-	return nr_reclaimed;
-}
-
 /*
  * This routine traverse page_cgroup in given list and drop them all.
  * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
@@ -4790,9 +4452,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
 		mz = &pn->zoneinfo[zone];
 		for_each_lru(lru)
 			INIT_LIST_HEAD(&mz->lruvec.lists[lru]);
-		mz->usage_in_excess = 0;
-		mz->on_tree = false;
-		mz->memcg = memcg;
 	}
 	memcg->info.nodeinfo[node] = pn;
 	return 0;
@@ -4867,7 +4526,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 {
 	int node;
 
-	mem_cgroup_remove_from_trees(memcg);
 	free_css_id(&mem_cgroup_subsys, &memcg->css);
 
 	for_each_node(node)
@@ -4923,41 +4581,6 @@ static void __init enable_swap_cgroup(void)
 }
 #endif
 
-static int mem_cgroup_soft_limit_tree_init(void)
-{
-	struct mem_cgroup_tree_per_node *rtpn;
-	struct mem_cgroup_tree_per_zone *rtpz;
-	int tmp, node, zone;
-
-	for_each_node(node) {
-		tmp = node;
-		if (!node_state(node, N_NORMAL_MEMORY))
-			tmp = -1;
-		rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, tmp);
-		if (!rtpn)
-			goto err_cleanup;
-
-		soft_limit_tree.rb_tree_per_node[node] = rtpn;
-
-		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-			rtpz = &rtpn->rb_tree_per_zone[zone];
-			rtpz->rb_root = RB_ROOT;
-			spin_lock_init(&rtpz->lock);
-		}
-	}
-	return 0;
-
-err_cleanup:
-	for_each_node(node) {
-		if (!soft_limit_tree.rb_tree_per_node[node])
-			break;
-		kfree(soft_limit_tree.rb_tree_per_node[node]);
-		soft_limit_tree.rb_tree_per_node[node] = NULL;
-	}
-	return 1;
-
-}
-
 static struct cgroup_subsys_state * __ref
 mem_cgroup_create(struct cgroup *cont)
 {
@@ -4978,8 +4601,6 @@ mem_cgroup_create(struct cgroup *cont)
 		int cpu;
 		enable_swap_cgroup();
 		parent = NULL;
-		if (mem_cgroup_soft_limit_tree_init())
-			goto free_out;
 		root_mem_cgroup = memcg;
 		for_each_possible_cpu(cpu) {
 			struct memcg_stock_pcp *stock =
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1a51868..a5f690b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2128,24 +2128,51 @@ restart:
 	throttle_vm_writeout(sc->gfp_mask);
 }
 
+static bool should_reclaim_mem_cgroup(struct mem_cgroup *target_mem_cgroup,
+				      struct mem_cgroup *memcg,
+				      int priority)
+{
+	/* Reclaim from mem_cgroup if any of these conditions are met:
+	 * - This is a global reclaim
+	 * - reclaim priority is higher than DEF_PRIORITY - 3
+	 * - mem_cgroup exceeds its soft limit
+	 *
+	 * The priority check is a balance of how hard to preserve the pages
+	 * under softlimit. If the memcgs of the zone having trouble to reclaim
+	 * pages above their softlimit, we have to reclaim under softlimit
+	 * instead of burning more cpu cycles.
+	 */
+	if (target_mem_cgroup || priority <= DEF_PRIORITY - 3 ||
+			mem_cgroup_soft_limit_exceeded(memcg))
+		return true;
+
+	return false;
+}
+
 static void shrink_zone(int priority, struct zone *zone,
 			struct scan_control *sc)
 {
 	struct mem_cgroup *root = sc->target_mem_cgroup;
-	struct mem_cgroup_reclaim_cookie reclaim = {
-		.zone = zone,
-		.priority = priority,
-	};
 	struct mem_cgroup *memcg;
+	int above_softlimit, ignore_softlimit = 0;
+
 
-	memcg = mem_cgroup_iter(root, NULL, &reclaim);
+restart:
+	above_softlimit = 0;
+	memcg = mem_cgroup_iter(root, NULL, NULL);
 	do {
 		struct mem_cgroup_zone mz = {
 			.mem_cgroup = memcg,
 			.zone = zone,
 		};
 
-		shrink_mem_cgroup_zone(priority, &mz, sc);
+		if (ignore_softlimit ||
+		   should_reclaim_mem_cgroup(root, memcg, priority)) {
+
+			shrink_mem_cgroup_zone(priority, &mz, sc);
+			above_softlimit = 1;
+		}
+
 		/*
 		 * Limit reclaim has historically picked one memcg and
 		 * scanned it with decreasing priority levels until
@@ -2160,8 +2187,13 @@ static void shrink_zone(int priority, struct zone *zone,
 			mem_cgroup_iter_break(root, memcg);
 			break;
 		}
-		memcg = mem_cgroup_iter(root, memcg, &reclaim);
+		memcg = mem_cgroup_iter(root, memcg, NULL);
 	} while (memcg);
+
+	if (!above_softlimit) {
+		ignore_softlimit = 1;
+		goto restart;
+	}
 }
 
 /* Returns true if compaction should go ahead for a high-order request */
@@ -2226,8 +2258,6 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
 {
 	struct zoneref *z;
 	struct zone *zone;
-	unsigned long nr_soft_reclaimed;
-	unsigned long nr_soft_scanned;
 	bool aborted_reclaim = false;
 
 	/*
@@ -2266,18 +2296,6 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
 					continue;
 				}
 			}
-			/*
-			 * This steals pages from memory cgroups over softlimit
-			 * and returns the number of reclaimed pages and
-			 * scanned pages. This works for global memory pressure
-			 * and balancing, not for a memcg's limit.
-			 */
-			nr_soft_scanned = 0;
-			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
-						sc->order, sc->gfp_mask,
-						&nr_soft_scanned);
-			sc->nr_reclaimed += nr_soft_reclaimed;
-			sc->nr_scanned += nr_soft_scanned;
 			/* need some check for avoid more shrink_zone() */
 		}
 
@@ -2457,47 +2475,6 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 
-unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
-						gfp_t gfp_mask, bool noswap,
-						struct zone *zone,
-						unsigned long *nr_scanned)
-{
-	struct scan_control sc = {
-		.nr_scanned = 0,
-		.nr_to_reclaim = SWAP_CLUSTER_MAX,
-		.may_writepage = !laptop_mode,
-		.may_unmap = 1,
-		.may_swap = !noswap,
-		.order = 0,
-		.target_mem_cgroup = memcg,
-	};
-	struct mem_cgroup_zone mz = {
-		.mem_cgroup = memcg,
-		.zone = zone,
-	};
-
-	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
-			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
-
-	trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
-						      sc.may_writepage,
-						      sc.gfp_mask);
-
-	/*
-	 * NOTE: Although we can get the priority field, using it
-	 * here is not a good idea, since it limits the pages we can scan.
-	 * if we don't reclaim here, the shrink_zone from balance_pgdat
-	 * will pick up pages from other mem cgroup's as well. We hack
-	 * the priority and make it zero.
-	 */
-	shrink_mem_cgroup_zone(0, &mz, &sc);
-
-	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
-
-	*nr_scanned = sc.nr_scanned;
-	return sc.nr_reclaimed;
-}
-
 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 					   gfp_t gfp_mask,
 					   bool noswap)
@@ -2672,8 +2649,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
 	unsigned long total_scanned;
 	struct reclaim_state *reclaim_state = current->reclaim_state;
-	unsigned long nr_soft_reclaimed;
-	unsigned long nr_soft_scanned;
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
 		.may_unmap = 1,
@@ -2776,16 +2751,6 @@ loop_again:
 
 			sc.nr_scanned = 0;
 
-			nr_soft_scanned = 0;
-			/*
-			 * Call soft limit reclaim before calling shrink_zone.
-			 */
-			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
-							order, sc.gfp_mask,
-							&nr_soft_scanned);
-			sc.nr_reclaimed += nr_soft_reclaimed;
-			total_scanned += nr_soft_scanned;
-
 			/*
 			 * We put equal pressure on every zone, unless
 			 * one zone has way too many pages free
-- 
1.7.7.3

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