Re: [PATCH] mm: memcontrol: Add the missing numa stat of anon and file for cgroup v2

[Shakeel Butt <shakeelb@google.com>]

On Thu, Sep 10, 2020 at 1:46 AM Muchun Song <songmuchun@bytedance.com> wrote:
>
> In the cgroup v1, we have a numa_stat interface. This is useful for
> providing visibility into the numa locality information within an
> memcg since the pages are allowed to be allocated from any physical
> node. One of the use cases is evaluating application performance by
> combining this information with the application's CPU allocation.
> But the cgroup v2 does not. So this patch adds the missing information.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---

I am actually working on exposing this info on v2 as well.

>  mm/memcontrol.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 75cd1a1e66c8..c779673f29b2 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1492,10 +1492,34 @@ static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
>         return false;
>  }
>
> +#ifdef CONFIG_NUMA
> +static unsigned long memcg_node_page_state(struct mem_cgroup *memcg,
> +                                          unsigned int nid,
> +                                          enum node_stat_item idx)
> +{
> +       long x;
> +       struct mem_cgroup_per_node *pn;
> +       struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
> +
> +       VM_BUG_ON(nid >= nr_node_ids);
> +
> +       pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> +       x = atomic_long_read(&pn->lruvec_stat[idx]);
> +#ifdef CONFIG_SMP
> +       if (x < 0)
> +               x = 0;
> +#endif
> +       return x;
> +}
> +#endif
> +
>  static char *memory_stat_format(struct mem_cgroup *memcg)
>  {
>         struct seq_buf s;
>         int i;
> +#ifdef CONFIG_NUMA
> +       int nid;
> +#endif
>
>         seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
>         if (!s.buffer)
> @@ -1512,12 +1536,30 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>          * Current memory state:
>          */
>

Let's not break the parsers of memory.stat. I would prefer a separate
interface like v1 i.e. memory.numa_stat.

> -       seq_buf_printf(&s, "anon %llu\n",
> +       seq_buf_printf(&s, "anon %llu",
>                        (u64)memcg_page_state(memcg, NR_ANON_MAPPED) *
>                        PAGE_SIZE);
> -       seq_buf_printf(&s, "file %llu\n",
> +#ifdef CONFIG_NUMA
> +       for_each_node_state(nid, N_MEMORY)
> +               seq_buf_printf(&s, " N%d=%llu", nid,
> +                              (u64)memcg_node_page_state(memcg, nid,
> +                                                         NR_ANON_MAPPED) *
> +                              PAGE_SIZE);
> +#endif
> +       seq_buf_putc(&s, '\n');
> +
> +       seq_buf_printf(&s, "file %llu",
>                        (u64)memcg_page_state(memcg, NR_FILE_PAGES) *
>                        PAGE_SIZE);
> +#ifdef CONFIG_NUMA
> +       for_each_node_state(nid, N_MEMORY)
> +               seq_buf_printf(&s, " N%d=%llu", nid,
> +                              (u64)memcg_node_page_state(memcg, nid,
> +                                                         NR_FILE_PAGES) *
> +                              PAGE_SIZE);
> +#endif
> +       seq_buf_putc(&s, '\n');
> +

The v1's numa_stat exposes the LRUs, why NR_ANON_MAPPED and NR_FILE_PAGES?

Also I think exposing slab_[un]reclaimable per node would be beneficial as well.

>         seq_buf_printf(&s, "kernel_stack %llu\n",
>                        (u64)memcg_page_state(memcg, NR_KERNEL_STACK_KB) *
>                        1024);
> --
> 2.20.1
>