Re: [External] Re: [PATCH v3] mm: memcontrol: Add the missing numa_stat interface for cgroup v2

[Muchun Song]

On Tue, Sep 15, 2020 at 12:07 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> On Sun, Sep 13, 2020 at 12:01 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > Suggested-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > ---
> [snip]
> > +
> > +static struct numa_stat numa_stats[] = {
> > +       { "anon", PAGE_SIZE, NR_ANON_MAPPED },
> > +       { "file", PAGE_SIZE, NR_FILE_PAGES },
> > +       { "kernel_stack", 1024, NR_KERNEL_STACK_KB },
> > +       { "shmem", PAGE_SIZE, NR_SHMEM },
> > +       { "file_mapped", PAGE_SIZE, NR_FILE_MAPPED },
> > +       { "file_dirty", PAGE_SIZE, NR_FILE_DIRTY },
> > +       { "file_writeback", PAGE_SIZE, NR_WRITEBACK },
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +       /*
> > +        * The ratio will be initialized in numa_stats_init(). Because
> > +        * on some architectures, the macro of HPAGE_PMD_SIZE is not
> > +        * constant(e.g. powerpc).
> > +        */
> > +       { "anon_thp", 0, NR_ANON_THPS },
> > +#endif
> > +       { "inactive_anon", PAGE_SIZE, NR_INACTIVE_ANON },
> > +       { "active_anon", PAGE_SIZE, NR_ACTIVE_ANON },
> > +       { "inactive_file", PAGE_SIZE, NR_INACTIVE_FILE },
> > +       { "active_file", PAGE_SIZE, NR_ACTIVE_FILE },
> > +       { "unevictable", PAGE_SIZE, NR_UNEVICTABLE },
> > +       { "slab_reclaimable", 1, NR_SLAB_RECLAIMABLE_B },
> > +       { "slab_unreclaimable", 1, NR_SLAB_UNRECLAIMABLE_B },
> > +};
> > +
> > +static int __init numa_stats_init(void)
> > +{
> > +       int i;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(numa_stats); i++) {
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +               if (numa_stats[i].idx == NR_ANON_THPS)
> > +                       numa_stats[i].ratio = HPAGE_PMD_SIZE;
> > +#endif
> > +       }
>
> The for loop seems excessive but I don't really have a good alternative.

Yeah, I also have no good alternative. The numa_stats is only initialized
once. So there may be no problem :).

>
> > +
> > +       return 0;
> > +}
> > +pure_initcall(numa_stats_init);
> > +
> > +static unsigned long memcg_node_page_state(struct mem_cgroup *memcg,
> > +                                          unsigned int nid,
> > +                                          enum node_stat_item idx)
> > +{
> > +       VM_BUG_ON(nid >= nr_node_ids);
> > +       return lruvec_page_state(mem_cgroup_lruvec(memcg, NODE_DATA(nid)), idx);
> > +}
> > +
> > +static const char *memory_numa_stat_format(struct mem_cgroup *memcg)
> > +{
> > +       int i;
> > +       struct seq_buf s;
> > +
> > +       /* Reserve a byte for the trailing null */
> > +       seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE - 1);
> > +       if (!s.buffer)
> > +               return NULL;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(numa_stats); i++) {
> > +               int nid;
> > +
> > +               seq_buf_printf(&s, "%s", numa_stats[i].name);
> > +               for_each_node_state(nid, N_MEMORY) {
> > +                       u64 size;
> > +
> > +                       size = memcg_node_page_state(memcg, nid,
> > +                                                    numa_stats[i].idx);
> > +                       size *= numa_stats[i].ratio;
> > +                       seq_buf_printf(&s, " N%d=%llu", nid, size);
> > +               }
> > +               seq_buf_putc(&s, '\n');
> > +       }
> > +
> > +       /* The above should easily fit into one page */
> > +       if (WARN_ON_ONCE(seq_buf_putc(&s, '\0')))
> > +               s.buffer[PAGE_SIZE - 1] = '\0';
>
> I think you should follow Michal's recommendation at
> http://lkml.kernel.org/r/20200914115724.GO16999@xxxxxxxxxxxxxx

Here is different, because the seq_buf_putc(&s, '\n') will not add \0 unless
we use seq_buf_puts(&s, "\n").


-- 
Yours,
Muchun