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Message-ID: <cc557aab0912271923v4a4ed8cco168193c63efd44f@mail.gmail.com>
Date: Mon, 28 Dec 2009 05:23:51 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: containers@...ts.linux-foundation.org, linux-mm@...ck.org,
Paul Menage <menage@...gle.com>,
Li Zefan <lizf@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Pavel Emelyanov <xemul@...nvz.org>,
Dan Malek <dan@...eddedalley.com>,
Vladislav Buzov <vbuzov@...eddedalley.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Alexander Shishkin <virtuoso@...nd.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] memcg: implement memory thresholds
On Mon, Dec 28, 2009 at 4:43 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Sun, 27 Dec 2009 04:09:02 +0200
> "Kirill A. Shutemov" <kirill@...temov.name> wrote:
>
>> 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@...temov.name>
>> ---
>> Documentation/cgroups/memory.txt | 19 +++-
>> mm/memcontrol.c | 275 ++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 293 insertions(+), 1 deletions(-)
>>
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index b871f25..195af07 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
>> @@ -414,7 +414,24 @@ NOTE1: Soft limits take effect over a long period of time, since they involve
>> NOTE2: It is recommended to set the soft limit always below the hard limit,
>> otherwise the hard limit will take precedence.
>>
>> -8. TODO
>> +8. Memory thresholds
>> +
>> +Memory controler implements memory thresholds using cgroups notification
>> +API (see cgroups.txt). It allows to register multiple memory and memsw
>> +thresholds and gets notifications when it crosses.
>> +
>> +To register a threshold application need:
>> + - create an eventfd using eventfd(2);
>> + - 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.
>> +
>> +9. TODO
>>
>> 1. Add support for accounting huge pages (as a separate controller)
>> 2. Make per-cgroup scanner reclaim not-shared pages first
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 36eb7af..3a0a6a1 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -6,6 +6,10 @@
>> * Copyright 2007 OpenVZ SWsoft Inc
>> * Author: Pavel Emelianov <xemul@...nvz.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
>> @@ -39,6 +43,8 @@
>> #include <linux/mm_inline.h>
>> #include <linux/page_cgroup.h>
>> #include <linux/cpu.h>
>> +#include <linux/eventfd.h>
>> +#include <linux/sort.h>
>> #include "internal.h"
>>
>> #include <asm/uaccess.h>
>> @@ -56,6 +62,7 @@ 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.
>> @@ -72,6 +79,8 @@ 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 +191,20 @@ 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 {
>> + unsigned int size;
>> + atomic_t cur;
>> + struct mem_cgroup_threshold entries[0];
>> +};
>> +
> Why "array" is a choice here ? IOW, why not list ?
We need be able to walk by thresholds in both directions to be fast.
AFAIK, It's impossible with RCU-protected list.
> How many waiters are expected as usual workload ?
Array of thresholds reads every 100 page in/out for every CPU.
Write access only when registering new threshold.
>> +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
>> @@ -233,6 +256,15 @@ 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;
>> +
>> /*
>> * statistics. This must be placed at the end of memcg.
>> */
>> @@ -525,6 +557,8 @@ 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();
>> }
>>
>> @@ -1510,6 +1544,8 @@ charged:
>> if (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);
>> @@ -2075,6 +2111,8 @@ __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);
>> @@ -3071,12 +3109,246 @@ 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(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 *thresholds;
>> + u64 usage = mem_cgroup_usage(memcg, swap);
>> + int i, cur;
>> +
>> + rcu_read_lock();
>> + if (!swap) {
>> + thresholds = rcu_dereference(memcg->thresholds);
>> + } else {
>> + thresholds = rcu_dereference(memcg->memsw_thresholds);
>> + }
>> +
>> + if (!thresholds)
>> + goto unlock;
>> +
>> + cur = atomic_read(&thresholds->cur);
>> +
>> + /* Check if a threshold crossed in any direction */
>> +
>> + for(i = cur; i >= 0 &&
>> + unlikely(thresholds->entries[i].threshold > usage); i--) {
>> + atomic_dec(&thresholds->cur);
>> + eventfd_signal(thresholds->entries[i].eventfd, 1);
>> + }
>> +
>> + for(i = cur + 1; i < thresholds->size &&
>> + unlikely(thresholds->entries[i].threshold <= usage); i++) {
>> + atomic_inc(&thresholds->cur);
>> + eventfd_signal(thresholds->entries[i].eventfd, 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->cur, -1);
>> + for(i = 0; i < size; i++) {
>> + if (thresholds_new->entries[i].threshold < usage)
>> + atomic_inc(&thresholds_new->cur);
>> + }
>> +
>> + /*
>> + * 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);
>> +
>> + synchronize_rcu();
>
> Could you add explanation when you use synchronize_rcu() ?
It uses before freeing old array of thresholds to be sure than nobody uses it.
>> + kfree(thresholds);
>
> Can't this be freed by RCU instead of synchronize_rcu() ?
Yes, this can. But I don't think that (un)registering os thresholds is
time critical.
I think my variant is more clean.
>> +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->cur, -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)
>> + atomic_inc(&thresholds_new->cur);
> It's better to do atomic set after loop.
We need one more counter to do this. Do you like it?
>> + j++;
>> + }
>
> Hmm..is this "copy array" usual coding style for handling eventfd ?
Since we store only pointer to struct eventfd_ctx, I don't see a problem.
>> +
>> +assign:
>> + if (type == _MEM)
>> + rcu_assign_pointer(memcg->thresholds, thresholds_new);
>> + else
>> + rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
>> +
>> + 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",
>> @@ -3128,6 +3400,8 @@ 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",
>> @@ -3367,6 +3641,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>> if (parent)
>> mem->swappiness = get_swappiness(parent);
>> atomic_set(&mem->refcnt, 1);
>> + mutex_init(&mem->thresholds_lock);
>> return &mem->css;
>> free_out:
>> __mem_cgroup_free(mem);
>> --
>> 1.6.5.7
>>
--
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