Re: [PATCH v2] mm: memcontrol: optimize per-lruvec stats counter memory usage
From: Shakeel Butt <hidden>
Date: 2020-12-08 18:21:24
Also in:
linux-mm, lkml
On Tue, Dec 8, 2020 at 1:53 AM Muchun Song [off-list ref] wrote:
The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), so the type of s32 of lruvec_stat_cpu is enough. And introduce struct per_cpu_lruvec_stat to optimize memory usage. The size of struct lruvec_stat is 304 bytes on 64 bits system. As it is a per-cpu structure. So with this patch, we can save 304 / 2 * ncpu bytes per-memcg per-node where ncpu is the number of the possible CPU. If there are c memory cgroup (include dying cgroup) and n NUMA node in the system. Finally, we can save (152 * ncpu * c * n) bytes. Signed-off-by: Muchun Song <redacted>
Few nits below: Reviewed-by: Shakeel Butt <redacted>
quoted hunk ↗ jump to hunk
--- Changes in v1 -> v2: - Update the commit log to point out how many bytes that we can save. include/linux/memcontrol.h | 6 +++++- mm/memcontrol.c | 10 +++++++++- 2 files changed, 14 insertions(+), 2 deletions(-)diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 3febf64d1b80..290d6ec8535a 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h@@ -92,6 +92,10 @@ struct lruvec_stat { long count[NR_VM_NODE_STAT_ITEMS]; }; +struct per_cpu_lruvec_stat {
lruvec_stat is also per-cpu, so the name per_cpu_lruvec_stat does not really tell why it is different from lruvec. Maybe name is batched_lruvec_stat or something else.
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+ s32 count[NR_VM_NODE_STAT_ITEMS]; +}; + /* * Bitmap of shrinker::id corresponding to memcg-aware shrinkers, * which have elements charged to this memcg.@@ -111,7 +115,7 @@ struct mem_cgroup_per_node { struct lruvec_stat __percpu *lruvec_stat_local;
A comment for the above why it still needs to be lruvec_stat.
quoted hunk ↗ jump to hunk
/* Subtree VM stats (batched updates) */ - struct lruvec_stat __percpu *lruvec_stat_cpu; + struct per_cpu_lruvec_stat __percpu *lruvec_stat_cpu; atomic_long_t lruvec_stat[NR_VM_NODE_STAT_ITEMS]; unsigned long lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];diff --git a/mm/memcontrol.c b/mm/memcontrol.c index eec44918d373..da6dc6ca388d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -5198,7 +5198,7 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node) return 1; } - pn->lruvec_stat_cpu = alloc_percpu_gfp(struct lruvec_stat, + pn->lruvec_stat_cpu = alloc_percpu_gfp(struct per_cpu_lruvec_stat, GFP_KERNEL_ACCOUNT); if (!pn->lruvec_stat_cpu) { free_percpu(pn->lruvec_stat_local);@@ -7089,6 +7089,14 @@ static int __init mem_cgroup_init(void) { int cpu, node; + /* + * Currently s32 type (can refer to struct per_cpu_lruvec_stat) is + * used for per-memcg-per-cpu caching of per-node statistics. In order + * to work fine, we should make sure that the overfill threshold can't + * exceed S32_MAX / PAGE_SIZE. + */ + BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S32_MAX / PAGE_SIZE); + cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL, memcg_hotplug_cpu_dead); --2.11.0