Re: [PATCH v1 3/5] mm: memcg/percpu: per-memcg percpu memory statistics

Dennis Zhou
2020-06-05T19:53:12Z

On Thu, May 28, 2020 at 04:25:06PM -0700, Roman Gushchin wrote:
> Percpu memory can represent a noticeable chunk of the total
> memory consumption, especially on big machines with many CPUs.
> Let's track percpu memory usage for each memcg and display
> it in memory.stat.
>
> A percpu allocation is usually scattered over multiple pages
> (and nodes), and can be significantly smaller than a page.
> So let's add a byte-sized counter on the memcg level:
> MEMCG_PERCPU_B. Byte-sized vmstat infra created for slabs
> can be perfectly reused for percpu case.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 4 ++++
> include/linux/memcontrol.h | 8 ++++++++
> mm/memcontrol.c | 4 +++-
> mm/percpu.c | 10 ++++++++++
> 4 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index fed4e1d2a343..aa8cb6dadadc 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1276,6 +1276,10 @@ PAGE_SIZE multiple when read back.
> Amount of memory used for storing in-kernel data
> structures.
>
> + percpu
> + Amount of memory used for storing per-cpu kernel
> + data structures.
> +
> sock
> Amount of memory used in network transmission buffers
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7a84d9164449..f62a95d472f7 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -32,11 +32,19 @@ struct kmem_cache;
> enum memcg_stat_item {
> MEMCG_SWAP = NR_VM_NODE_STAT_ITEMS,
> MEMCG_SOCK,
> + MEMCG_PERCPU_B,
> /* XXX: why are these zone and not node counters? */
> MEMCG_KERNEL_STACK_KB,
> MEMCG_NR_STAT,
> };
>
> +static __always_inline bool memcg_stat_item_in_bytes(enum memcg_stat_item item)
> +{
> + if (item == MEMCG_PERCPU_B)
> + return true;
> + return vmstat_item_in_bytes(item);
> +}
> +
> enum memcg_memory_event {
> MEMCG_LOW,
> MEMCG_HIGH,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7bc3fd196210..5007d1585a4a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -783,7 +783,7 @@ void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
> if (mem_cgroup_disabled())
> return;
>
> - if (vmstat_item_in_bytes(idx))
> + if (memcg_stat_item_in_bytes(idx))
> threshold <<= PAGE_SHIFT;
>
> x = val + __this_cpu_read(memcg->vmstats_percpu->stat[idx]);
> @@ -1490,6 +1490,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
> seq_buf_printf(&s, "slab %llu\n",
> (u64)(memcg_page_state(memcg, NR_SLAB_RECLAIMABLE_B) +
> memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE_B)));
> + seq_buf_printf(&s, "percpu %llu\n",
> + (u64)memcg_page_state(memcg, MEMCG_PERCPU_B));
> seq_buf_printf(&s, "sock %llu\n",
> (u64)memcg_page_state(memcg, MEMCG_SOCK) *
> PAGE_SIZE);
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 85f5755c9114..b4b3e9c8a6d1 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1608,6 +1608,11 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
>
> if (chunk) {
> chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = objcg;
> +
> + rcu_read_lock();
> + mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
> + size * num_possible_cpus());
> + rcu_read_unlock();
> } else {
> obj_cgroup_uncharge(objcg, size * num_possible_cpus());
> obj_cgroup_put(objcg);
> @@ -1626,6 +1631,11 @@ static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
>
> obj_cgroup_uncharge(objcg, size * num_possible_cpus());
>
> + rcu_read_lock();
> + mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
> + -(size * num_possible_cpus()));
> + rcu_read_unlock();
> +
> obj_cgroup_put(objcg);