@@ -112,6 +112,9 @@ struct lruvec_stats {
/* Aggregated (CPU and subtree) state */
long state[NR_VM_NODE_STAT_ITEMS];
+ /* Non-hierarchical (CPU aggregated) state */
+ long state_local[NR_VM_NODE_STAT_ITEMS];
+
/* Pending child counts during tree propagation */
long state_pending[NR_VM_NODE_STAT_ITEMS];
};
@@ -1020,14 +1023,12 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
{
struct mem_cgroup_per_node *pn;
long x = 0;
- int cpu;
if (mem_cgroup_disabled())
return node_page_state(lruvec_pgdat(lruvec), idx);
pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
- for_each_possible_cpu(cpu)
- x += per_cpu(pn->lruvec_stats_percpu->state[idx], cpu);
+ x = READ_ONCE(pn->lruvec_stats.state_local[idx]);
#ifdef CONFIG_SMP
if (x < 0)
x = 0;
@@ -742,6 +742,10 @@ struct memcg_vmstats {
long state[MEMCG_NR_STAT];
unsigned long events[NR_MEMCG_EVENTS];
+ /* Non-hierarchical (CPU aggregated) page state & events */
+ long state_local[MEMCG_NR_STAT];
+ unsigned long events_local[NR_MEMCG_EVENTS];
+
/* Pending child counts during tree propagation */
long state_pending[MEMCG_NR_STAT];
unsigned long events_pending[NR_MEMCG_EVENTS];
@@ -775,11 +779,8 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
/* idx can be of type enum memcg_stat_item or node_stat_item. */
static unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)
{
- long x = 0;
- int cpu;
+ long x = READ_ONCE(memcg->vmstats->state_local[idx]);
- for_each_possible_cpu(cpu)
- x += per_cpu(memcg->vmstats_percpu->state[idx], cpu);
#ifdef CONFIG_SMP
if (x < 0)
x = 0;
@@ -926,16 +927,12 @@ static unsigned long memcg_events(struct mem_cgroup *memcg, int event)
static unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
{
- long x = 0;
- int cpu;
int index = memcg_events_index(event);
if (index < 0)
return 0;
- for_each_possible_cpu(cpu)
- x += per_cpu(memcg->vmstats_percpu->events[index], cpu);
- return x;
+ return READ_ONCE(memcg->vmstats->events_local[index]);
}
static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
@@ -5526,7 +5523,7 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
struct mem_cgroup *parent = parent_mem_cgroup(memcg);
struct memcg_vmstats_percpu *statc;
- long delta, v;
+ long delta, delta_cpu, v;
int i, nid;
statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
@@ -5542,9 +5539,11 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
memcg->vmstats->state_pending[i] = 0;
/* Add CPU changes on this level since the last flush */
+ delta_cpu = 0;
v = READ_ONCE(statc->state[i]);
if (v != statc->state_prev[i]) {
- delta += v - statc->state_prev[i];
+ delta_cpu = v - statc->state_prev[i];
+ delta += delta_cpu;
statc->state_prev[i] = v;
}
@@ -5553,6 +5552,7 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
/* Aggregate counts on this level and propagate upwards */
memcg->vmstats->state[i] += delta;
+ memcg->vmstats->state_local[i] += delta_cpu;
if (parent)
parent->vmstats->state_pending[i] += delta;
}
@@ -5562,9 +5562,11 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
if (delta)
memcg->vmstats->events_pending[i] = 0;
+ delta_cpu = 0;
v = READ_ONCE(statc->events[i]);
if (v != statc->events_prev[i]) {
- delta += v - statc->events_prev[i];
+ delta_cpu = v - statc->events_prev[i];
+ delta += delta_cpu;
statc->events_prev[i] = v;
}
@@ -5572,6 +5574,7 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
continue;
memcg->vmstats->events[i] += delta;
+ memcg->vmstats->events_local[i] += delta_cpu;
if (parent)
parent->vmstats->events_pending[i] += delta;
}
@@ -5591,9 +5594,11 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
if (delta)
pn->lruvec_stats.state_pending[i] = 0;
+ delta_cpu = 0;
v = READ_ONCE(lstatc->state[i]);
if (v != lstatc->state_prev[i]) {
- delta += v - lstatc->state_prev[i];
+ delta_cpu = v - lstatc->state_prev[i];
+ delta += delta_cpu;
lstatc->state_prev[i] = v;
}
@@ -5601,6 +5606,7 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
continue;
pn->lruvec_stats.state[i] += delta;
+ pn->lruvec_stats.state_local[i] += delta_cpu;
if (ppn)
ppn->lruvec_stats.state_pending[i] += delta;
}
@@ -664,6 +664,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
struct lruvec *lruvec;
int i;
+ mem_cgroup_flush_stats();
lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
pages += lruvec_page_state_local(lruvec,
Currently, memcg uses rstat to maintain hierarchical stats. The rstat framework keeps track of which cgroups have updates on which cpus. For non-hierarchical stats, as memcg moved to rstat, they are no longer readily available as counters. Instead, the percpu counters for a given stat need to be summed to get the non-hierarchical stat value. This causes a performance regression when reading non-hierarchical stats on kernels where memcg moved to using rstat. This is especially visible when reading memory.stat on cgroup v1. There are also some code paths internal to the kernel that read such non-hierarchical stats. It is inefficient to iterate and sum counters in all cpus when the rstat framework knows exactly when a percpu counter has an update. Instead, maintain cpu-aggregated non-hierarchical counters for each stat. During an rstat flush, keep those updated as well. When reading non-hierarchical stats, we no longer need to iterate cpus, we just need to read the maintainer counters, similar to hierarchical stats. A caveat is that we now a stats flush before reading local/non-hierarchical stats through {memcg/lruvec}_page_state_local() or memcg_events_local(), where we previously only needed a flush to read hierarchical stats. Most contexts reading non-hierarchical stats are already doing a flush, add a flush to the only missing context in count_shadow_nodes(). With this patch, reading memory.stat from 1000 memcgs is 3x faster on a machine with 256 cpus on cgroup v1: # for i in $(seq 1000); do mkdir /sys/fs/cgroup/memory/cg$i; done # time cat /dev/cgroup/memory/cg*/memory.stat > /dev/null real 0m0.125s user 0m0.005s sys 0m0.120s After: real 0m0.032s user 0m0.005s sys 0m0.027s Signed-off-by: Yosry Ahmed <yosryahmed@google.com> --- include/linux/memcontrol.h | 7 ++++--- mm/memcontrol.c | 32 +++++++++++++++++++------------- mm/workingset.c | 1 + 3 files changed, 24 insertions(+), 16 deletions(-)