Re: [PATCH 7/7] mm: memcontrol: consolidate lruvec stat flushing
flat view
From: Michal Hocko <mhocko@suse.com>
Date: 2021-02-05 23:51:32
Also in:
cgroups, lkml
On Tue 02-02-21 13:47:46, Johannes Weiner wrote:
There are two functions to flush the per-cpu data of an lruvec into the rest of the cgroup tree: when the cgroup is being freed, and when a CPU disappears during hotplug. The difference is whether all CPUs or just one is being collected, but the rest of the flushing code is the same. Merge them into one function and share the common code.
IIUC the only reason for the cpu == -1 special case is to avoid zeroying, right? Is this optimization worth the special case? The code would be slightly easier to follow without this.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Anyway the above is not really a fundamental objection. It is more important to unify the flushing. Acked-by: Michal Hocko <mhocko@suse.com>
quoted hunk ↗ jump to hunk
--- mm/memcontrol.c | 88 +++++++++++++++++++++++-------------------------- 1 file changed, 42 insertions(+), 46 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b205b2413186..88e8afc49a46 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -2410,39 +2410,56 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) mutex_unlock(&percpu_charge_mutex); } -static int memcg_hotplug_cpu_dead(unsigned int cpu) +static void memcg_flush_lruvec_page_state(struct mem_cgroup *memcg, int cpu) { - struct memcg_stock_pcp *stock; - struct mem_cgroup *memcg; - - stock = &per_cpu(memcg_stock, cpu); - drain_stock(stock); + int nid; - for_each_mem_cgroup(memcg) { + for_each_node(nid) { + struct mem_cgroup_per_node *pn = memcg->nodeinfo[nid]; + unsigned long stat[NR_VM_NODE_STAT_ITEMS] = { 0, }; + struct batched_lruvec_stat *lstatc; int i; - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) { - int nid; - - for_each_node(nid) { - struct batched_lruvec_stat *lstatc; - struct mem_cgroup_per_node *pn; - long x; - - pn = memcg->nodeinfo[nid]; + if (cpu == -1) { + int cpui; + /* + * The memcg is about to be freed, collect all + * CPUs, no need to zero anything out. + */ + for_each_online_cpu(cpui) { + lstatc = per_cpu_ptr(pn->lruvec_stat_cpu, cpui); + for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) + stat[i] += lstatc->count[i]; + } + } else { + /* + * The CPU has gone away, collect and zero out + * its stats, it may come back later. + */ + for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) { lstatc = per_cpu_ptr(pn->lruvec_stat_cpu, cpu); - - x = lstatc->count[i]; + stat[i] = lstatc->count[i]; lstatc->count[i] = 0; - - if (x) { - do { - atomic_long_add(x, &pn->lruvec_stat[i]); - } while ((pn = parent_nodeinfo(pn, nid))); - } } } + + do { + for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) + atomic_long_add(stat[i], &pn->lruvec_stat[i]); + } while ((pn = parent_nodeinfo(pn, nid))); } +} + +static int memcg_hotplug_cpu_dead(unsigned int cpu) +{ + struct memcg_stock_pcp *stock; + struct mem_cgroup *memcg; + + stock = &per_cpu(memcg_stock, cpu); + drain_stock(stock); + + for_each_mem_cgroup(memcg) + memcg_flush_lruvec_page_state(memcg, cpu); return 0; }@@ -3636,27 +3653,6 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css, } } -static void memcg_flush_lruvec_page_state(struct mem_cgroup *memcg) -{ - int node; - - for_each_node(node) { - struct mem_cgroup_per_node *pn = memcg->nodeinfo[node]; - unsigned long stat[NR_VM_NODE_STAT_ITEMS] = {0, }; - struct mem_cgroup_per_node *pi; - int cpu, i; - - for_each_online_cpu(cpu) - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) - stat[i] += per_cpu( - pn->lruvec_stat_cpu->count[i], cpu); - - for (pi = pn; pi; pi = parent_nodeinfo(pi, node)) - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) - atomic_long_add(stat[i], &pi->lruvec_stat[i]); - } -} - #ifdef CONFIG_MEMCG_KMEM static int memcg_online_kmem(struct mem_cgroup *memcg) {@@ -5197,7 +5193,7 @@ static void mem_cgroup_free(struct mem_cgroup *memcg) * Flush percpu lruvec stats to guarantee the value * correctness on parent's and all ancestor levels. */ - memcg_flush_lruvec_page_state(memcg); + memcg_flush_lruvec_page_state(memcg, -1); __mem_cgroup_free(memcg); }-- 2.30.0
-- Michal Hocko SUSE Labs