mm: memcontrol: revert use of root_mem_cgroup res_counter
Dave Hansen reports a massive scalability regression in an uncontained
page fault benchmark with more than 30 concurrent threads, which he
bisected down to 05b843012335 ("mm: memcontrol: use root_mem_cgroup
res_counter") and pin-pointed on res_counter spinlock contention.
That change relied on the per-cpu charge caches to mostly swallow the
res_counter costs, but it's apparent that the caches don't scale yet.
Revert memcg back to bypassing res_counters on the root level in order
to restore performance for uncontained workloads.
Reported-by: Dave Hansen <dave@sr71.net>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ec4dcf1..085dc6d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2534,6 +2534,8 @@
unsigned long long size;
int ret = 0;
+ if (mem_cgroup_is_root(memcg))
+ goto done;
retry:
if (consume_stock(memcg, nr_pages))
goto done;
@@ -2611,9 +2613,7 @@
if (!(gfp_mask & __GFP_NOFAIL))
return -ENOMEM;
bypass:
- memcg = root_mem_cgroup;
- ret = -EINTR;
- goto retry;
+ return -EINTR;
done_restock:
if (batch > nr_pages)
@@ -2626,6 +2626,9 @@
{
unsigned long bytes = nr_pages * PAGE_SIZE;
+ if (mem_cgroup_is_root(memcg))
+ return;
+
res_counter_uncharge(&memcg->res, bytes);
if (do_swap_account)
res_counter_uncharge(&memcg->memsw, bytes);
@@ -2640,6 +2643,9 @@
{
unsigned long bytes = nr_pages * PAGE_SIZE;
+ if (mem_cgroup_is_root(memcg))
+ return;
+
res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
if (do_swap_account)
res_counter_uncharge_until(&memcg->memsw,
@@ -4093,6 +4099,46 @@
return retval;
}
+static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *memcg,
+ enum mem_cgroup_stat_index idx)
+{
+ struct mem_cgroup *iter;
+ long val = 0;
+
+ /* Per-cpu values can be negative, use a signed accumulator */
+ for_each_mem_cgroup_tree(iter, memcg)
+ val += mem_cgroup_read_stat(iter, idx);
+
+ if (val < 0) /* race ? */
+ val = 0;
+ return val;
+}
+
+static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
+{
+ u64 val;
+
+ if (!mem_cgroup_is_root(memcg)) {
+ if (!swap)
+ return res_counter_read_u64(&memcg->res, RES_USAGE);
+ else
+ return res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ }
+
+ /*
+ * Transparent hugepages are still accounted for in MEM_CGROUP_STAT_RSS
+ * as well as in MEM_CGROUP_STAT_RSS_HUGE.
+ */
+ val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
+ val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS);
+
+ if (swap)
+ val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_SWAP);
+
+ return val << PAGE_SHIFT;
+}
+
+
static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
@@ -4102,8 +4148,12 @@
switch (type) {
case _MEM:
+ if (name == RES_USAGE)
+ return mem_cgroup_usage(memcg, false);
return res_counter_read_u64(&memcg->res, name);
case _MEMSWAP:
+ if (name == RES_USAGE)
+ return mem_cgroup_usage(memcg, true);
return res_counter_read_u64(&memcg->memsw, name);
case _KMEM:
return res_counter_read_u64(&memcg->kmem, name);
@@ -4572,10 +4622,7 @@
if (!t)
goto unlock;
- if (!swap)
- usage = res_counter_read_u64(&memcg->res, RES_USAGE);
- else
- usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ usage = mem_cgroup_usage(memcg, swap);
/*
* current_threshold points to threshold just below or equal to usage.
@@ -4673,10 +4720,10 @@
if (type == _MEM) {
thresholds = &memcg->thresholds;
- usage = res_counter_read_u64(&memcg->res, RES_USAGE);
+ usage = mem_cgroup_usage(memcg, false);
} else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
- usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ usage = mem_cgroup_usage(memcg, true);
} else
BUG();
@@ -4762,10 +4809,10 @@
if (type == _MEM) {
thresholds = &memcg->thresholds;
- usage = res_counter_read_u64(&memcg->res, RES_USAGE);
+ usage = mem_cgroup_usage(memcg, false);
} else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
- usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ usage = mem_cgroup_usage(memcg, true);
} else
BUG();
@@ -5525,9 +5572,9 @@
* core guarantees its existence.
*/
} else {
- res_counter_init(&memcg->res, &root_mem_cgroup->res);
- res_counter_init(&memcg->memsw, &root_mem_cgroup->memsw);
- res_counter_init(&memcg->kmem, &root_mem_cgroup->kmem);
+ res_counter_init(&memcg->res, NULL);
+ res_counter_init(&memcg->memsw, NULL);
+ res_counter_init(&memcg->kmem, NULL);
/*
* Deeper hierachy with use_hierarchy == false doesn't make
* much sense so let cgroup subsystem know about this
@@ -5969,8 +6016,9 @@
/* we must fixup refcnts and charges */
if (mc.moved_swap) {
/* uncharge swap account from the old cgroup */
- res_counter_uncharge(&mc.from->memsw,
- PAGE_SIZE * mc.moved_swap);
+ if (!mem_cgroup_is_root(mc.from))
+ res_counter_uncharge(&mc.from->memsw,
+ PAGE_SIZE * mc.moved_swap);
for (i = 0; i < mc.moved_swap; i++)
css_put(&mc.from->css);
@@ -5979,8 +6027,9 @@
* we charged both to->res and to->memsw, so we should
* uncharge to->res.
*/
- res_counter_uncharge(&mc.to->res,
- PAGE_SIZE * mc.moved_swap);
+ if (!mem_cgroup_is_root(mc.to))
+ res_counter_uncharge(&mc.to->res,
+ PAGE_SIZE * mc.moved_swap);
/* we've already done css_get(mc.to) */
mc.moved_swap = 0;
}
@@ -6345,7 +6394,8 @@
rcu_read_lock();
memcg = mem_cgroup_lookup(id);
if (memcg) {
- res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+ if (!mem_cgroup_is_root(memcg))
+ res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
mem_cgroup_swap_statistics(memcg, false);
css_put(&memcg->css);
}
@@ -6509,12 +6559,15 @@
{
unsigned long flags;
- if (nr_mem)
- res_counter_uncharge(&memcg->res, nr_mem * PAGE_SIZE);
- if (nr_memsw)
- res_counter_uncharge(&memcg->memsw, nr_memsw * PAGE_SIZE);
-
- memcg_oom_recover(memcg);
+ if (!mem_cgroup_is_root(memcg)) {
+ if (nr_mem)
+ res_counter_uncharge(&memcg->res,
+ nr_mem * PAGE_SIZE);
+ if (nr_memsw)
+ res_counter_uncharge(&memcg->memsw,
+ nr_memsw * PAGE_SIZE);
+ memcg_oom_recover(memcg);
+ }
local_irq_save(flags);
__this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS], nr_anon);
