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    Subject[PATCH 1/7] mm: memcontrol: fix cpuhotplug statistics flushing
    Date
    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>
    ---
    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
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