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: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a730c91..6587f65 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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 @@
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 @@
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
@@ -1259,6 +1263,133 @@
}
/*
+ * 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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
/* 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);