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Commit cdec2e42 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: coalesce charging via percpu storage 



This is a patch for coalescing access to res_counter at charging by percpu
caching.  At charge, memcg charges 64pages and remember it in percpu
cache.  Because it's cache, drain/flush if necessary.

This version uses public percpu area.
 2 benefits for using public percpu area.
 1. Sum of stocked charge in the system is limited to # of cpus
    not to the number of memcg. This shows better synchonization.
 2. drain code for flush/cpuhotplug is very easy (and quick)

The most important point of this patch is that we never touch res_counter
in fast path. The res_counter is system-wide shared counter which is modified
very frequently. We shouldn't touch it as far as we can for avoiding
false sharing.

On x86-64 8cpu server, I tested overheads of memcg at page fault by
running a program which does map/fault/unmap in a loop. Running
a task per a cpu by taskset and see sum of the number of page faults
in 60secs.

[without memcg config]
  40156968  page-faults              #      0.085 M/sec   ( +-   0.046% )
  27.67 cache-miss/faults

[root cgroup]
  36659599  page-faults              #      0.077 M/sec   ( +-   0.247% )
  31.58 cache miss/faults

[in a child cgroup]
  18444157  page-faults              #      0.039 M/sec   ( +-   0.133% )
  69.96 cache miss/faults

[ + coalescing uncharge patch]
  27133719  page-faults              #      0.057 M/sec   ( +-   0.155% )
  47.16 cache miss/faults

[ + coalescing uncharge patch + this patch ]
  34224709  page-faults              #      0.072 M/sec   ( +-   0.173% )
  34.69 cache miss/faults

Changelog (since Oct/2):
  - updated comments
  - replaced get_cpu_var() with __get_cpu_var() if possible.
  - removed mutex for system-wide drain. adds a counter instead of it.
  - removed CONFIG_HOTPLUG_CPU

Changelog (old):
  - rebased onto the latest mmotm
  - moved charge size check before __GFP_WAIT check for avoiding unnecesary
  - added asynchronous flush routine.
  - fixed bugs pointed out by Nishimura-san.

[akpm@linux-foundation.org: tweak comments]
[nishimura@mxp.nes.nec.co.jp: don't do INIT_WORK() repeatedly against the same work_struct]
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 569b846d

mm/memcontrol.c

+156 −6
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ 
#include <linux/vmalloc.h>

#include <linux/mm_inline.h>

#include <linux/page_cgroup.h>

#include <linux/cpu.h>

#include "internal.h"



#include <asm/uaccess.h>
@@ -275,6 +276,7 @@ enum charge_type { 
static void mem_cgroup_get(struct mem_cgroup *mem);

static void mem_cgroup_put(struct mem_cgroup *mem);

static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);

static void drain_all_stock_async(void);



static struct mem_cgroup_per_zone *

mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
@@ -1137,6 +1139,8 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, 
		victim = mem_cgroup_select_victim(root_mem);

		if (victim == root_mem) {

			loop++;

			if (loop >= 1)

				drain_all_stock_async();

			if (loop >= 2) {

				/*

				 * If we have not been able to reclaim
@@ -1258,6 +1262,133 @@ done: 
	unlock_page_cgroup(pc);

}



/*

 * size of first charge trial. "32" comes from vmscan.c's magic value.

 * TODO: maybe necessary to use big numbers in big irons.

 */

#define CHARGE_SIZE	(32 * PAGE_SIZE)

struct memcg_stock_pcp {

	struct mem_cgroup *cached; /* this never be root cgroup */

	int charge;

	struct work_struct work;

};

static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);

static atomic_t memcg_drain_count;



/*

 * Try to consume stocked charge on this cpu. If success, PAGE_SIZE is consumed

 * from local stock and true is returned. If the stock is 0 or charges from a

 * cgroup which is not current target, returns false. This stock will be

 * refilled.

 */

static bool consume_stock(struct mem_cgroup *mem)

{

	struct memcg_stock_pcp *stock;

	bool ret = true;



	stock = &get_cpu_var(memcg_stock);

	if (mem == stock->cached && stock->charge)

		stock->charge -= PAGE_SIZE;

	else /* need to call res_counter_charge */

		ret = false;

	put_cpu_var(memcg_stock);

	return ret;

}



/*

 * Returns stocks cached in percpu to res_counter and reset cached information.

 */

static void drain_stock(struct memcg_stock_pcp *stock)

{

	struct mem_cgroup *old = stock->cached;



	if (stock->charge) {

		res_counter_uncharge(&old->res, stock->charge);

		if (do_swap_account)

			res_counter_uncharge(&old->memsw, stock->charge);

	}

	stock->cached = NULL;

	stock->charge = 0;

}



/*

 * This must be called under preempt disabled or must be called by

 * a thread which is pinned to local cpu.

 */

static void drain_local_stock(struct work_struct *dummy)

{

	struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);

	drain_stock(stock);

}



/*

 * Cache charges(val) which is from res_counter, to local per_cpu area.

 * This will be consumed by consumt_stock() function, later.

 */

static void refill_stock(struct mem_cgroup *mem, int val)

{

	struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);



	if (stock->cached != mem) { /* reset if necessary */

		drain_stock(stock);

		stock->cached = mem;

	}

	stock->charge += val;

	put_cpu_var(memcg_stock);

}



/*

 * Tries to drain stocked charges in other cpus. This function is asynchronous

 * and just put a work per cpu for draining localy on each cpu. Caller can

 * expects some charges will be back to res_counter later but cannot wait for

 * it.

 */

static void drain_all_stock_async(void)

{

	int cpu;

	/* This function is for scheduling "drain" in asynchronous way.

	 * The result of "drain" is not directly handled by callers. Then,

	 * if someone is calling drain, we don't have to call drain more.

	 * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if

	 * there is a race. We just do loose check here.

	 */

	if (atomic_read(&memcg_drain_count))

		return;

	/* Notify other cpus that system-wide "drain" is running */

	atomic_inc(&memcg_drain_count);

	get_online_cpus();

	for_each_online_cpu(cpu) {

		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);

		schedule_work_on(cpu, &stock->work);

	}

 	put_online_cpus();

	atomic_dec(&memcg_drain_count);

	/* We don't wait for flush_work */

}



/* This is a synchronous drain interface. */

static void drain_all_stock_sync(void)

{

	/* called when force_empty is called */

	atomic_inc(&memcg_drain_count);

	schedule_on_each_cpu(drain_local_stock);

	atomic_dec(&memcg_drain_count);

}



static int __cpuinit memcg_stock_cpu_callback(struct notifier_block *nb,

					unsigned long action,

					void *hcpu)

{

	int cpu = (unsigned long)hcpu;

	struct memcg_stock_pcp *stock;



	if (action != CPU_DEAD)

		return NOTIFY_OK;

	stock = &per_cpu(memcg_stock, cpu);

	drain_stock(stock);

	return NOTIFY_OK;

}



/*

 * Unlike exported interface, "oom" parameter is added. if oom==true,

 * oom-killer can be invoked.
@@ -1269,6 +1400,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
	struct mem_cgroup *mem, *mem_over_limit;

	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;

	struct res_counter *fail_res;

	int csize = CHARGE_SIZE;



	if (unlikely(test_thread_flag(TIF_MEMDIE))) {

		/* Don't account this! */
@@ -1293,23 +1425,25 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
		return 0;



	VM_BUG_ON(css_is_removed(&mem->css));

	if (mem_cgroup_is_root(mem))

		goto done;



	while (1) {

		int ret = 0;

		unsigned long flags = 0;



		if (mem_cgroup_is_root(mem))

			goto done;

		ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);

		if (consume_stock(mem))

			goto charged;



		ret = res_counter_charge(&mem->res, csize, &fail_res);

		if (likely(!ret)) {

			if (!do_swap_account)

				break;

			ret = res_counter_charge(&mem->memsw, PAGE_SIZE,

							&fail_res);

			ret = res_counter_charge(&mem->memsw, csize, &fail_res);

			if (likely(!ret))

				break;

			/* mem+swap counter fails */

			res_counter_uncharge(&mem->res, PAGE_SIZE);

			res_counter_uncharge(&mem->res, csize);

			flags |= MEM_CGROUP_RECLAIM_NOSWAP;

			mem_over_limit = mem_cgroup_from_res_counter(fail_res,

									memsw);
@@ -1318,6 +1452,11 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
			mem_over_limit = mem_cgroup_from_res_counter(fail_res,

									res);



		/* reduce request size and retry */

		if (csize > PAGE_SIZE) {

			csize = PAGE_SIZE;

			continue;

		}

		if (!(gfp_mask & __GFP_WAIT))

			goto nomem;
@@ -1347,6 +1486,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
			goto nomem;

		}

	}

	if (csize > PAGE_SIZE)

		refill_stock(mem, csize - PAGE_SIZE);

charged:

	/*

	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.

	 * if they exceeds softlimit.
@@ -2469,6 +2611,7 @@ move_account: 
			goto out;

		/* This is for making all *used* pages to be on LRU. */

		lru_add_drain_all();

		drain_all_stock_sync();

		ret = 0;

		for_each_node_state(node, N_HIGH_MEMORY) {

			for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
@@ -3183,11 +3326,18 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont) 


	/* root ? */

	if (cont->parent == NULL) {

		int cpu;

		enable_swap_cgroup();

		parent = NULL;

		root_mem_cgroup = mem;

		if (mem_cgroup_soft_limit_tree_init())

			goto free_out;

		for_each_possible_cpu(cpu) {

			struct memcg_stock_pcp *stock =

						&per_cpu(memcg_stock, cpu);

			INIT_WORK(&stock->work, drain_local_stock);

		}

		hotcpu_notifier(memcg_stock_cpu_callback, 0);



	} else {

		parent = mem_cgroup_from_cont(cont->parent);