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

[Shakeel Butt <shakeelb@google.com>]

On Mon, Sep 14, 2020 at 9:55 AM Muchun Song <songmuchun@bytedance.com> wrote:
>
> On Tue, Sep 15, 2020 at 12:07 AM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > On Sun, Sep 13, 2020 at 12:01 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>
> > > Suggested-by: Shakeel Butt <shakeelb@google.com>
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > ---
> > [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@dhcp22.suse.cz
>
> Here is different, because the seq_buf_putc(&s, '\n') will not add \0 unless
> we use seq_buf_puts(&s, "\n").
>

Why a separate memory_numa_stat_format()? For memory_stat_format(), it
is called from two places. There is no need to have a separate
memory_numa_stat_format(). Similarly why not just call seq_printf()
instead of formatting into a seq_buf?