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SubjectRe: [PATCH 1/7] mm: memcontrol: fix cpuhotplug statistics flushing
On Tue 02-02-21 13:47:40, Johannes Weiner wrote:
> The memcg hotunplug callback erroneously flushes counts on the local
> CPU, not the counts of the CPU going away; those counts will be lost.
>
> Flush the CPU that is actually going away.
>
> Also simplify the code a bit by using mod_memcg_state() and
> count_memcg_events() instead of open-coding the upward flush - this is
> comparable to how vmstat.c handles hotunplug flushing.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

Shakeel has already pointed out Fixes.

> ---
> mm/memcontrol.c | 35 +++++++++++++++++++++--------------
> 1 file changed, 21 insertions(+), 14 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ed5cc78a8dbf..8120d565dd79 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2411,45 +2411,52 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
> static int memcg_hotplug_cpu_dead(unsigned int cpu)
> {
> struct memcg_stock_pcp *stock;
> - struct mem_cgroup *memcg, *mi;
> + struct mem_cgroup *memcg;
>
> stock = &per_cpu(memcg_stock, cpu);
> drain_stock(stock);
>
> for_each_mem_cgroup(memcg) {
> + struct memcg_vmstats_percpu *statc;
> int i;
>
> + statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
> +
> for (i = 0; i < MEMCG_NR_STAT; i++) {
> int nid;
> - long x;
>
> - x = this_cpu_xchg(memcg->vmstats_percpu->stat[i], 0);
> - if (x)
> - for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
> - atomic_long_add(x, &memcg->vmstats[i]);
> + if (statc->stat[i]) {
> + mod_memcg_state(memcg, i, statc->stat[i]);
> + statc->stat[i] = 0;
> + }
>
> if (i >= NR_VM_NODE_STAT_ITEMS)
> continue;
>
> for_each_node(nid) {
> + struct batched_lruvec_stat *lstatc;
> struct mem_cgroup_per_node *pn;
> + long x;
>
> pn = mem_cgroup_nodeinfo(memcg, nid);
> - x = this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0);
> - if (x)
> + lstatc = per_cpu_ptr(pn->lruvec_stat_cpu, cpu);
> +
> + x = lstatc->count[i];
> + lstatc->count[i] = 0;
> +
> + if (x) {
> do {
> atomic_long_add(x, &pn->lruvec_stat[i]);
> } while ((pn = parent_nodeinfo(pn, nid)));
> + }
> }
> }
>
> for (i = 0; i < NR_VM_EVENT_ITEMS; i++) {
> - long x;
> -
> - x = this_cpu_xchg(memcg->vmstats_percpu->events[i], 0);
> - if (x)
> - for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
> - atomic_long_add(x, &memcg->vmevents[i]);
> + if (statc->events[i]) {
> + count_memcg_events(memcg, i, statc->events[i]);
> + statc->events[i] = 0;
> + }
> }
> }
>
> --
> 2.30.0
>

--
Michal Hocko
SUSE Labs

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