memcg: implement memory thresholds

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.

[akpm@linux-foundation.org: coding-style fixes]
[nishimura@mxp.nes.nec.co.jp: fix documentation merge issue]
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Dan Malek <dan@embeddedalley.com>
Cc: Vladislav Buzov <vbuzov@embeddedalley.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 309 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5a41d93c7077..649df435b8e2 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
@@ -35,6 +39,8 @@
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/spinlock.h>
+#include <linux/eventfd.h>
+#include <linux/sort.h>
 #include <linux/fs.h>
 #include <linux/seq_file.h>
 #include <linux/vmalloc.h>
@@ -58,6 +64,7 @@ static int really_do_swap_account __initdata = 1; /* for remember boot option*/
 #endif
 
 #define SOFTLIMIT_EVENTS_THRESH (1000)
+#define THRESHOLDS_EVENTS_THRESH (100)
 
 /*
  * Statistics for memory cgroup.
@@ -74,6 +81,8 @@ 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,
 };
@@ -177,6 +186,23 @@ struct mem_cgroup_tree {
 
 static struct mem_cgroup_tree soft_limit_tree __read_mostly;
 
+struct mem_cgroup_threshold {
+        struct eventfd_ctx *eventfd;
+        u64 threshold;
+};
+
+struct mem_cgroup_threshold_ary {
+        /* An array index points to threshold just below usage. */
+        atomic_t current_threshold;
+        /* Size of entries[] */
+        unsigned int size;
+        /* Array of thresholds */
+        struct mem_cgroup_threshold entries[0];
+};
+
+static bool mem_cgroup_threshold_check(struct mem_cgroup *mem);
+static void mem_cgroup_threshold(struct mem_cgroup *mem);
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
@@ -228,6 +254,15 @@ struct mem_cgroup {
         /* set when res.limit == memsw.limit */
         bool            memsw_is_minimum;
 
+        /* protect arrays of thresholds */
+        struct mutex thresholds_lock;
+
+        /* thresholds for memory usage. RCU-protected */
+        struct mem_cgroup_threshold_ary *thresholds;
+
+        /* thresholds for mem+swap usage. RCU-protected */
+        struct mem_cgroup_threshold_ary *memsw_thresholds;
+
         /*
          * Should we move charges of a task when a task is moved into this
          * mem_cgroup ? And what type of charges should we move ?
@@ -549,6 +584,8 @@ 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();
 }
 
@@ -1576,6 +1613,8 @@ charged:
         if (page && mem_cgroup_soft_limit_check(mem))
                 mem_cgroup_update_tree(mem, page);
 done:
+        if (mem_cgroup_threshold_check(mem))
+                mem_cgroup_threshold(mem);
         return 0;
 nomem:
         css_put(&mem->css);
@@ -2148,6 +2187,8 @@ __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);
         /* at swapout, this memcg will be accessed to record to swap */
         if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
                 css_put(&mem->css);
@@ -3232,12 +3273,277 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
         return 0;
 }
 
+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_safe(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_ary *t;
+        u64 usage;
+        int i;
+
+        rcu_read_lock();
+        if (!swap)
+                t = rcu_dereference(memcg->thresholds);
+        else
+                t = rcu_dereference(memcg->memsw_thresholds);
+
+        if (!t)
+                goto unlock;
+
+        usage = mem_cgroup_usage(memcg, swap);
+
+        /*
+         * current_threshold points to threshold just below usage.
+         * If it's not true, a threshold was crossed after last
+         * call of __mem_cgroup_threshold().
+         */
+        i = atomic_read(&t->current_threshold);
+
+        /*
+         * Iterate backward over array of thresholds starting from
+         * current_threshold and check if a threshold is crossed.
+         * If none of thresholds below usage is crossed, we read
+         * only one element of the array here.
+         */
+        for (; i >= 0 && unlikely(t->entries[i].threshold > usage); i--)
+                eventfd_signal(t->entries[i].eventfd, 1);
+
+        /* i = current_threshold + 1 */
+        i++;
+
+        /*
+         * Iterate forward over array of thresholds starting from
+         * current_threshold+1 and check if a threshold is crossed.
+         * If none of thresholds above usage is crossed, we read
+         * only one element of the array here.
+         */
+        for (; i < t->size && unlikely(t->entries[i].threshold <= usage); i++)
+                eventfd_signal(t->entries[i].eventfd, 1);
+
+        /* Update current_threshold */
+        atomic_set(&t->current_threshold, i - 1);
+unlock:
+        rcu_read_unlock();
+}
+
+static void mem_cgroup_threshold(struct mem_cgroup *memcg)
+{
+        __mem_cgroup_threshold(memcg, false);
+        if (do_swap_account)
+                __mem_cgroup_threshold(memcg, true);
+}
+
+static int compare_thresholds(const void *a, const void *b)
+{
+        const struct mem_cgroup_threshold *_a = a;
+        const struct mem_cgroup_threshold *_b = b;
+
+        return _a->threshold - _b->threshold;
+}
+
+static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
+                struct eventfd_ctx *eventfd, const char *args)
+{
+        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
+        struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
+        int type = MEMFILE_TYPE(cft->private);
+        u64 threshold, usage;
+        int size;
+        int i, ret;
+
+        ret = res_counter_memparse_write_strategy(args, &threshold);
+        if (ret)
+                return ret;
+
+        mutex_lock(&memcg->thresholds_lock);
+        if (type == _MEM)
+                thresholds = memcg->thresholds;
+        else if (type == _MEMSWAP)
+                thresholds = memcg->memsw_thresholds;
+        else
+                BUG();
+
+        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
+
+        /* Check if a threshold crossed before adding a new one */
+        if (thresholds)
+                __mem_cgroup_threshold(memcg, type == _MEMSWAP);
+
+        if (thresholds)
+                size = thresholds->size + 1;
+        else
+                size = 1;
+
+        /* Allocate memory for new array of thresholds */
+        thresholds_new = kmalloc(sizeof(*thresholds_new) +
+                        size * sizeof(struct mem_cgroup_threshold),
+                        GFP_KERNEL);
+        if (!thresholds_new) {
+                ret = -ENOMEM;
+                goto unlock;
+        }
+        thresholds_new->size = size;
+
+        /* Copy thresholds (if any) to new array */
+        if (thresholds)
+                memcpy(thresholds_new->entries, thresholds->entries,
+                                thresholds->size *
+                                sizeof(struct mem_cgroup_threshold));
+        /* Add new threshold */
+        thresholds_new->entries[size - 1].eventfd = eventfd;
+        thresholds_new->entries[size - 1].threshold = threshold;
+
+        /* Sort thresholds. Registering of new threshold isn't time-critical */
+        sort(thresholds_new->entries, size,
+                        sizeof(struct mem_cgroup_threshold),
+                        compare_thresholds, NULL);
+
+        /* Find current threshold */
+        atomic_set(&thresholds_new->current_threshold, -1);
+        for (i = 0; i < size; i++) {
+                if (thresholds_new->entries[i].threshold < usage) {
+                        /*
+                         * thresholds_new->current_threshold will not be used
+                         * until rcu_assign_pointer(), so it's safe to increment
+                         * it here.
+                         */
+                        atomic_inc(&thresholds_new->current_threshold);
+                }
+        }
+
+        /*
+         * We need to increment refcnt to be sure that all thresholds
+         * will be unregistered before calling __mem_cgroup_free()
+         */
+        mem_cgroup_get(memcg);
+
+        if (type == _MEM)
+                rcu_assign_pointer(memcg->thresholds, thresholds_new);
+        else
+                rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
+
+        /* To be sure that nobody uses thresholds before freeing it */
+        synchronize_rcu();
+
+        kfree(thresholds);
+unlock:
+        mutex_unlock(&memcg->thresholds_lock);
+
+        return ret;
+}
+
+static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft,
+                struct eventfd_ctx *eventfd)
+{
+        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
+        struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
+        int type = MEMFILE_TYPE(cft->private);
+        u64 usage;
+        int size = 0;
+        int i, j, ret;
+
+        mutex_lock(&memcg->thresholds_lock);
+        if (type == _MEM)
+                thresholds = memcg->thresholds;
+        else if (type == _MEMSWAP)
+                thresholds = memcg->memsw_thresholds;
+        else
+                BUG();
+
+        /*
+         * Something went wrong if we trying to unregister a threshold
+         * if we don't have thresholds
+         */
+        BUG_ON(!thresholds);
+
+        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
+
+        /* Check if a threshold crossed before removing */
+        __mem_cgroup_threshold(memcg, type == _MEMSWAP);
+
+        /* Calculate new number of threshold */
+        for (i = 0; i < thresholds->size; i++) {
+                if (thresholds->entries[i].eventfd != eventfd)
+                        size++;
+        }
+
+        /* Set thresholds array to NULL if we don't have thresholds */
+        if (!size) {
+                thresholds_new = NULL;
+                goto assign;
+        }
+
+        /* Allocate memory for new array of thresholds */
+        thresholds_new = kmalloc(sizeof(*thresholds_new) +
+                        size * sizeof(struct mem_cgroup_threshold),
+                        GFP_KERNEL);
+        if (!thresholds_new) {
+                ret = -ENOMEM;
+                goto unlock;
+        }
+        thresholds_new->size = size;
+
+        /* Copy thresholds and find current threshold */
+        atomic_set(&thresholds_new->current_threshold, -1);
+        for (i = 0, j = 0; i < thresholds->size; i++) {
+                if (thresholds->entries[i].eventfd == eventfd)
+                        continue;
+
+                thresholds_new->entries[j] = thresholds->entries[i];
+                if (thresholds_new->entries[j].threshold < usage) {
+                        /*
+                         * thresholds_new->current_threshold will not be used
+                         * until rcu_assign_pointer(), so it's safe to increment
+                         * it here.
+                         */
+                        atomic_inc(&thresholds_new->current_threshold);
+                }
+                j++;
+        }
+
+assign:
+        if (type == _MEM)
+                rcu_assign_pointer(memcg->thresholds, thresholds_new);
+        else
+                rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
+
+        /* To be sure that nobody uses thresholds before freeing it */
+        synchronize_rcu();
+
+        for (i = 0; i < thresholds->size - size; i++)
+                mem_cgroup_put(memcg);
+
+        kfree(thresholds);
+unlock:
+        mutex_unlock(&memcg->thresholds_lock);
+
+        return ret;
+}
 
 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",
@@ -3294,6 +3600,8 @@ 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",
@@ -3538,6 +3846,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
                 mem->swappiness = get_swappiness(parent);
         atomic_set(&mem->refcnt, 1);
         mem->move_charge_at_immigrate = 0;
+        mutex_init(&mem->thresholds_lock);
         return &mem->css;
 free_out:
         __mem_cgroup_free(mem);