[PATCH RFC v2 4/4] memcg: implement memory thresholds

["Kirill A. Shutemov" <kirill@shutemov.name>]

It allows to register multiple memory and memsw thresholds and gets
notifications when it crosses.

To register a threshold application need:
- create an eventfd;
- open memory.usage_in_bytes or memory.memsw.usage_in_bytes;
- write string like "<event_fd> <memory.usage_in_bytes> <threshold>" to
  cgroup.event_control.

Application will be notified through eventfd when memory usage crosses
threshold in any direction.

It's applicable for root and non-root cgroup.

It uses stats to track memory usage, simmilar to soft limits. It checks
if we need to send event to userspace on every 100 page in/out. I guess
it's good compromise between performance and accuracy of thresholds.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 mm/memcontrol.c |  263 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 263 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c6081cc..5ba2140 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6,6 +6,10 @@
  * Copyright 2007 OpenVZ SWsoft Inc
  * Author: Pavel Emelianov <xemul@openvz.org>
  *
+ * Memory thresholds
+ * Copyright (C) 2009 Nokia Corporation
+ * Author: Kirill A. Shutemov
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
@@ -38,6 +42,7 @@
 #include <linux/vmalloc.h>
 #include <linux/mm_inline.h>
 #include <linux/page_cgroup.h>
+#include <linux/eventfd.h>
 #include "internal.h"
 
 #include <asm/uaccess.h>
@@ -56,6 +61,7 @@ static int really_do_swap_account __initdata = 1; /* for remember boot option*/
 
 static DEFINE_MUTEX(memcg_tasklist);	/* can be hold under cgroup_mutex */
 #define SOFTLIMIT_EVENTS_THRESH (1000)
+#define THRESHOLDS_EVENTS_THRESH (100)
 
 /*
  * Statistics for memory cgroup.
@@ -72,6 +78,8 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
 	MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
 					used by soft limit implementation */
+	MEM_CGROUP_STAT_THRESHOLDS, /* decrements on each page in/out.
+					used by threshold implementation */
 
 	MEM_CGROUP_STAT_NSTATS,
 };
@@ -182,6 +190,15 @@ struct mem_cgroup_tree {
 
 static struct mem_cgroup_tree soft_limit_tree __read_mostly;
 
+struct mem_cgroup_threshold {
+	struct list_head list;
+	struct eventfd_ctx *eventfd;
+	u64 threshold;
+};
+
+static bool mem_cgroup_threshold_check(struct mem_cgroup* mem);
+static void mem_cgroup_threshold(struct mem_cgroup* mem, bool swap);
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
@@ -233,6 +250,19 @@ struct mem_cgroup {
 	/* set when res.limit == memsw.limit */
 	bool		memsw_is_minimum;
 
+	/* protect lists of thresholds*/
+	spinlock_t thresholds_lock;
+
+	/* thresholds for memory usage */
+	struct list_head thresholds;
+	struct mem_cgroup_threshold *below_threshold;
+	struct mem_cgroup_threshold *above_threshold;
+
+	/* thresholds for mem+swap usage */
+	struct list_head memsw_thresholds;
+	struct mem_cgroup_threshold *memsw_below_threshold;
+	struct mem_cgroup_threshold *memsw_above_threshold;
+
 	/*
 	 * statistics. This must be placed at the end of memcg.
 	 */
@@ -519,6 +549,8 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
 		__mem_cgroup_stat_add_safe(cpustat,
 				MEM_CGROUP_STAT_PGPGOUT_COUNT, 1);
 	__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_SOFTLIMIT, -1);
+	__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_THRESHOLDS, -1);
+
 	put_cpu();
 }
 
@@ -1363,6 +1395,11 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 	if (mem_cgroup_soft_limit_check(mem))
 		mem_cgroup_update_tree(mem, page);
 done:
+	if (mem_cgroup_threshold_check(mem)) {
+		mem_cgroup_threshold(mem, false);
+		if (do_swap_account)
+			mem_cgroup_threshold(mem, true);
+	}
 	return 0;
 nomem:
 	css_put(&mem->css);
@@ -1906,6 +1943,11 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
 	if (mem_cgroup_soft_limit_check(mem))
 		mem_cgroup_update_tree(mem, page);
+	if (mem_cgroup_threshold_check(mem)) {
+		mem_cgroup_threshold(mem, false);
+		if (do_swap_account)
+			mem_cgroup_threshold(mem, true);
+	}
 	/* at swapout, this memcg will be accessed to record to swap */
 	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
 		css_put(&mem->css);
@@ -2860,11 +2902,181 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
 }
 
 
+static bool mem_cgroup_threshold_check(struct mem_cgroup *mem)
+{
+	bool ret = false;
+	int cpu;
+	s64 val;
+	struct mem_cgroup_stat_cpu *cpustat;
+
+	cpu = get_cpu();
+	cpustat = &mem->stat.cpustat[cpu];
+	val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_THRESHOLDS);
+	if (unlikely(val < 0)) {
+		__mem_cgroup_stat_set(cpustat, MEM_CGROUP_STAT_THRESHOLDS,
+				THRESHOLDS_EVENTS_THRESH);
+		ret = true;
+	}
+	put_cpu();
+	return ret;
+}
+
+static void mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
+{
+	struct mem_cgroup_threshold **below, **above;
+	struct list_head *thresholds;
+	u64 usage = mem_cgroup_usage(memcg, swap);
+
+	if (!swap) {
+		thresholds = &memcg->thresholds;
+		above = &memcg->above_threshold;
+		below = &memcg->below_threshold;
+	} else {
+		thresholds = &memcg->memsw_thresholds;
+		above = &memcg->memsw_above_threshold;
+		below = &memcg->memsw_below_threshold;
+	}
+
+	spin_lock(&memcg->thresholds_lock);
+	if ((*above)->threshold <= usage) {
+		*below = *above;
+		list_for_each_entry_continue((*above), thresholds, list) {
+			eventfd_signal((*below)->eventfd, 1);
+			if ((*above)->threshold > usage)
+				break;
+			*below = *above;
+		}
+	} else if ((*below)->threshold > usage) {
+		*above = *below;
+		list_for_each_entry_continue_reverse((*below), thresholds,
+				list) {
+			eventfd_signal((*above)->eventfd, 1);
+			if ((*below)->threshold <= usage)
+				break;
+			*above = *below;
+		}
+	}
+	spin_unlock(&memcg->thresholds_lock);
+}
+
+static void mem_cgroup_invalidate_thresholds(struct mem_cgroup *memcg,
+		bool swap)
+{
+	struct list_head *thresholds;
+	struct mem_cgroup_threshold **below, **above;
+	u64 usage = mem_cgroup_usage(memcg, swap);
+
+	if (!swap) {
+		thresholds = &memcg->thresholds;
+		above = &memcg->above_threshold;
+		below = &memcg->below_threshold;
+	} else {
+		thresholds = &memcg->memsw_thresholds;
+		above = &memcg->memsw_above_threshold;
+		below = &memcg->memsw_below_threshold;
+	}
+
+	*below = NULL;
+	list_for_each_entry((*above), thresholds, list) {
+		if ((*above)->threshold > usage) {
+			BUG_ON(!*below);
+			break;
+		}
+		*below = *above;
+	}
+}
+
+static inline struct mem_cgroup_threshold *mem_cgroup_threshold_alloc(void)
+{
+	struct mem_cgroup_threshold *new;
+
+	new = kmalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return NULL;
+	INIT_LIST_HEAD(&new->list);
+
+	return new;
+}
+
+static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
+		struct eventfd_ctx *eventfd, const char *args)
+{
+	u64 threshold;
+	struct mem_cgroup_threshold *new, *tmp;
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
+	struct list_head *thresholds;
+	int type = MEMFILE_TYPE(cft->private);
+	int ret;
+
+	ret = res_counter_memparse_write_strategy(args, &threshold);
+	if (ret)
+		return ret;
+
+	new = mem_cgroup_threshold_alloc();
+	if (!new)
+		return -ENOMEM;
+	new->eventfd = eventfd;
+	new->threshold = threshold;
+
+	if (type == _MEM)
+		thresholds = &memcg->thresholds;
+	else if (type == _MEMSWAP)
+		thresholds = &memcg->memsw_thresholds;
+	else
+		BUG();
+
+	/* Check if a threshold crossed before adding a new one */
+	mem_cgroup_threshold(memcg, type == _MEMSWAP);
+
+	spin_lock(&memcg->thresholds_lock);
+	list_for_each_entry(tmp, thresholds, list)
+		if (new->threshold < tmp->threshold) {
+			list_add_tail(&new->list, &tmp->list);
+			break;
+		}
+	mem_cgroup_invalidate_thresholds(memcg, type == _MEMSWAP);
+	spin_unlock(&memcg->thresholds_lock);
+
+	return 0;
+}
+
+static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft,
+		struct eventfd_ctx *eventfd)
+{
+	struct mem_cgroup_threshold *threshold, *tmp;
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
+	struct list_head *thresholds;
+	int type = MEMFILE_TYPE(cft->private);
+
+	if (type == _MEM)
+		thresholds = &memcg->thresholds;
+	else if (type == _MEMSWAP)
+		thresholds = &memcg->memsw_thresholds;
+	else
+		BUG();
+
+	/* Check if a threshold crossed before adding a new one */
+	mem_cgroup_threshold(memcg, type == _MEMSWAP);
+
+	spin_lock(&memcg->thresholds_lock);
+	list_for_each_entry_safe(threshold, tmp, thresholds, list)
+		if (threshold->eventfd == eventfd) {
+			list_del(&threshold->list);
+			kfree(threshold);
+		}
+	mem_cgroup_invalidate_thresholds(memcg, type == _MEMSWAP);
+	spin_unlock(&memcg->thresholds_lock);
+
+	return 0;
+}
+
 static struct cftype mem_cgroup_files[] = {
 	{
 		.name = "usage_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
 		.read_u64 = mem_cgroup_read,
+		.register_event = mem_cgroup_register_event,
+		.unregister_event = mem_cgroup_unregister_event,
 	},
 	{
 		.name = "max_usage_in_bytes",
@@ -2916,6 +3128,8 @@ static struct cftype memsw_cgroup_files[] = {
 		.name = "memsw.usage_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
 		.read_u64 = mem_cgroup_read,
+		.register_event = mem_cgroup_register_event,
+		.unregister_event = mem_cgroup_unregister_event,
 	},
 	{
 		.name = "memsw.max_usage_in_bytes",
@@ -2990,6 +3204,48 @@ static void free_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
 	kfree(mem->info.nodeinfo[node]);
 }
 
+static int mem_cgroup_thresholds_init(struct mem_cgroup *mem)
+{
+	INIT_LIST_HEAD(&mem->thresholds);
+	INIT_LIST_HEAD(&mem->memsw_thresholds);
+
+	mem->below_threshold = mem_cgroup_threshold_alloc();
+	list_add(&mem->below_threshold->list, &mem->thresholds);
+	mem->below_threshold->threshold = 0ULL;
+
+	mem->above_threshold = mem_cgroup_threshold_alloc();
+	list_add_tail(&mem->above_threshold->list, &mem->thresholds);
+	mem->above_threshold->threshold = RESOURCE_MAX;
+
+	mem->memsw_below_threshold = mem_cgroup_threshold_alloc();
+	list_add(&mem->memsw_below_threshold->list, &mem->memsw_thresholds);
+	mem->memsw_below_threshold->threshold = 0ULL;
+
+	mem->memsw_above_threshold = mem_cgroup_threshold_alloc();
+	list_add_tail(&mem->memsw_above_threshold->list, &mem->memsw_thresholds);
+	mem->memsw_above_threshold->threshold = RESOURCE_MAX;
+
+	return 0;
+}
+
+static void mem_cgroup_thresholds_free(struct mem_cgroup *mem)
+{
+	/* Make sure that lists have only two elements */
+	BUG_ON((mem->below_threshold) &&
+			(mem->above_threshold) &&
+			(mem->below_threshold->list.next !=
+			 &mem->above_threshold->list));
+	BUG_ON((mem->memsw_below_threshold) &&
+			(mem->memsw_above_threshold) &&
+			(mem->below_threshold->list.next !=
+			 &mem->above_threshold->list));
+
+	kfree(mem->below_threshold);
+	kfree(mem->above_threshold);
+	kfree(mem->memsw_below_threshold);
+	kfree(mem->memsw_above_threshold);
+}
+
 static int mem_cgroup_size(void)
 {
 	int cpustat_size = nr_cpu_ids * sizeof(struct mem_cgroup_stat_cpu);
@@ -3026,6 +3282,8 @@ static void __mem_cgroup_free(struct mem_cgroup *mem)
 {
 	int node;
 
+	mem_cgroup_thresholds_free(mem);
+
 	mem_cgroup_remove_from_trees(mem);
 	free_css_id(&mem_cgroup_subsys, &mem->css);
 
@@ -3145,6 +3403,11 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	mem->last_scanned_child = 0;
 	spin_lock_init(&mem->reclaim_param_lock);
 
+	spin_lock_init(&mem->thresholds_lock);
+	error = mem_cgroup_thresholds_init(mem);
+	if (error)
+		goto free_out;
+
 	if (parent)
 		mem->swappiness = get_swappiness(parent);
 	atomic_set(&mem->refcnt, 1);
-- 
1.6.5.3

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