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authorJohannes Weiner <hannes@cmpxchg.org>2019-06-13 15:55:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-06-13 17:34:56 -1000
commit815744d75152078cde5391fc1e3c2d4424323fb6 (patch)
tree6ac3ca02fd88a2bcef7024ef6dd005ee29621164 /mm
parentc11fb13a117e5a6736481c779cb971249ed96016 (diff)
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mm: memcontrol: don't batch updates of local VM stats and events
The kernel test robot noticed a 26% will-it-scale pagefault regression from commit 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty"). This appears to be caused by bouncing the additional cachelines from the new hierarchical statistics counters. We can fix this by getting rid of the batched local counters instead. Originally, there were *only* group-local counters, and they were fully maintained per cpu. A reader of a stats file high up in the cgroup tree would have to walk the entire subtree and collect each level's per-cpu counters to get the recursive view. This was prohibitively expensive, and so we switched to per-cpu batched updates of the local counters during a983b5ebee57 ("mm: memcontrol: fix excessive complexity in memory.stat reporting"), reducing the complexity from nr_subgroups * nr_cpus to nr_subgroups. With growing machines and cgroup trees, the tree walk itself became too expensive for monitoring top-level groups, and this is when the culprit patch added hierarchy counters on each cgroup level. When the per-cpu batch size would be reached, both the local and the hierarchy counters would get batch-updated from the per-cpu delta simultaneously. This makes local and hierarchical counter reads blazingly fast, but it unfortunately makes the write-side too cache line intense. Since local counter reads were never a problem - we only centralized them to accelerate the hierarchy walk - and use of the local counters are becoming rarer due to replacement with hierarchical views (ongoing rework in the page reclaim and workingset code), we can make those local counters unbatched per-cpu counters again. The scheme will then be as such: when a memcg statistic changes, the writer will: - update the local counter (per-cpu) - update the batch counter (per-cpu). If the batch is full: - spill the batch into the group's atomic_t - spill the batch into all ancestors' atomic_ts - empty out the batch counter (per-cpu) when a local memcg counter is read, the reader will: - collect the local counter from all cpus when a hiearchy memcg counter is read, the reader will: - read the atomic_t We might be able to simplify this further and make the recursive counters unbatched per-cpu counters as well (batch upward propagation, but leave per-cpu collection to the readers), but that will require a more in-depth analysis and testing of all the callsites. Deal with the immediate regression for now. Link: http://lkml.kernel.org/r/20190521151647.GB2870@cmpxchg.org Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty") Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-by: kernel test robot <rong.a.chen@intel.com> Tested-by: kernel test robot <rong.a.chen@intel.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Shakeel Butt <shakeelb@google.com> Cc: Roman Gushchin <guro@fb.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c41
1 files changed, 28 insertions, 13 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ca0bc6e6be13..ba9138a4a1de 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -691,11 +691,12 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
if (mem_cgroup_disabled())
return;
+ __this_cpu_add(memcg->vmstats_local->stat[idx], val);
+
x = val + __this_cpu_read(memcg->vmstats_percpu->stat[idx]);
if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
struct mem_cgroup *mi;
- atomic_long_add(x, &memcg->vmstats_local[idx]);
for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
atomic_long_add(x, &mi->vmstats[idx]);
x = 0;
@@ -745,11 +746,12 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
__mod_memcg_state(memcg, idx, val);
/* Update lruvec */
+ __this_cpu_add(pn->lruvec_stat_local->count[idx], val);
+
x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]);
if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
struct mem_cgroup_per_node *pi;
- atomic_long_add(x, &pn->lruvec_stat_local[idx]);
for (pi = pn; pi; pi = parent_nodeinfo(pi, pgdat->node_id))
atomic_long_add(x, &pi->lruvec_stat[idx]);
x = 0;
@@ -771,11 +773,12 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
if (mem_cgroup_disabled())
return;
+ __this_cpu_add(memcg->vmstats_local->events[idx], count);
+
x = count + __this_cpu_read(memcg->vmstats_percpu->events[idx]);
if (unlikely(x > MEMCG_CHARGE_BATCH)) {
struct mem_cgroup *mi;
- atomic_long_add(x, &memcg->vmevents_local[idx]);
for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
atomic_long_add(x, &mi->vmevents[idx]);
x = 0;
@@ -790,7 +793,12 @@ static unsigned long memcg_events(struct mem_cgroup *memcg, int event)
static unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
{
- return atomic_long_read(&memcg->vmevents_local[event]);
+ long x = 0;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ x += per_cpu(memcg->vmstats_local->events[event], cpu);
+ return x;
}
static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
@@ -2191,11 +2199,9 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
long x;
x = this_cpu_xchg(memcg->vmstats_percpu->stat[i], 0);
- if (x) {
- atomic_long_add(x, &memcg->vmstats_local[i]);
+ if (x)
for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
atomic_long_add(x, &memcg->vmstats[i]);
- }
if (i >= NR_VM_NODE_STAT_ITEMS)
continue;
@@ -2205,12 +2211,10 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
pn = mem_cgroup_nodeinfo(memcg, nid);
x = this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0);
- if (x) {
- atomic_long_add(x, &pn->lruvec_stat_local[i]);
+ if (x)
do {
atomic_long_add(x, &pn->lruvec_stat[i]);
} while ((pn = parent_nodeinfo(pn, nid)));
- }
}
}
@@ -2218,11 +2222,9 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
long x;
x = this_cpu_xchg(memcg->vmstats_percpu->events[i], 0);
- if (x) {
- atomic_long_add(x, &memcg->vmevents_local[i]);
+ if (x)
for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
atomic_long_add(x, &memcg->vmevents[i]);
- }
}
}
@@ -4483,8 +4485,15 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
if (!pn)
return 1;
+ pn->lruvec_stat_local = alloc_percpu(struct lruvec_stat);
+ if (!pn->lruvec_stat_local) {
+ kfree(pn);
+ return 1;
+ }
+
pn->lruvec_stat_cpu = alloc_percpu(struct lruvec_stat);
if (!pn->lruvec_stat_cpu) {
+ free_percpu(pn->lruvec_stat_local);
kfree(pn);
return 1;
}
@@ -4506,6 +4515,7 @@ static void free_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
return;
free_percpu(pn->lruvec_stat_cpu);
+ free_percpu(pn->lruvec_stat_local);
kfree(pn);
}
@@ -4516,6 +4526,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
for_each_node(node)
free_mem_cgroup_per_node_info(memcg, node);
free_percpu(memcg->vmstats_percpu);
+ free_percpu(memcg->vmstats_local);
kfree(memcg);
}
@@ -4544,6 +4555,10 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
if (memcg->id.id < 0)
goto fail;
+ memcg->vmstats_local = alloc_percpu(struct memcg_vmstats_percpu);
+ if (!memcg->vmstats_local)
+ goto fail;
+
memcg->vmstats_percpu = alloc_percpu(struct memcg_vmstats_percpu);
if (!memcg->vmstats_percpu)
goto fail;