linux-kernel - Re: [External] Re: [PATCH] mm/memcontrol: make the slab calculation consistent

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Date:   Thu, 3 Dec 2020 10:53:33 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH] mm/memcontrol: make the slab calculation consistent

On Thu, Dec 3, 2020 at 5:16 AM Roman Gushchin <guro@...com> wrote:
>
> On Wed, Dec 02, 2020 at 08:14:34PM +0800, Muchun Song wrote:
> > Although the ratio of the slab is one, we also should read the ratio
> > from the related memory_stats instead of hard-coding. And the local
> > variable of size is already the value of slab_unreclaimable. So we
> > do not need to read again. Simplify the code here.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > ---
> >  mm/memcontrol.c | 22 +++++++++++++++++-----
> >  1 file changed, 17 insertions(+), 5 deletions(-)
>
> Hi Muchun!
>
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 9922f1510956..03a9c64560f6 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1545,12 +1545,22 @@ static int __init memory_stats_init(void)
> >       int i;
> >
> >       for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
> > +             switch (memory_stats[i].idx) {
> >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > -             if (memory_stats[i].idx == NR_ANON_THPS ||
> > -                 memory_stats[i].idx == NR_FILE_THPS ||
> > -                 memory_stats[i].idx == NR_SHMEM_THPS)
> > +             case NR_ANON_THPS:
> > +             case NR_FILE_THPS:
> > +             case NR_SHMEM_THPS:
> >                       memory_stats[i].ratio = HPAGE_PMD_SIZE;
> > +                     break;
> >  #endif
> > +             case NR_SLAB_UNRECLAIMABLE_B:
> > +                     VM_BUG_ON(i < 1);
> > +                     VM_BUG_ON(memory_stats[i - 1].idx != NR_SLAB_RECLAIMABLE_B);
>
> Please, convert these to BUILD_BUG_ON(), they don't have to be runtime checks.

Agree. But here we cannot use BUILD_BUG_ON(). The compiler will
complain about it.

>
>
> > +                     break;
> > +             default:
> > +                     break;
> > +             }
> > +
> >               VM_BUG_ON(!memory_stats[i].ratio);
> >               VM_BUG_ON(memory_stats[i].idx >= MEMCG_NR_STAT);
> >       }
> > @@ -1587,8 +1597,10 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
> >               seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size);
> >
>
> Can you, please, add a small comment here stating that we're printing
> unreclaimable, reclaimable and the sum of both? It will simplify the reading of the code.

Will do.

>
> >               if (unlikely(memory_stats[i].idx == NR_SLAB_UNRECLAIMABLE_B)) {
> > -                     size = memcg_page_state(memcg, NR_SLAB_RECLAIMABLE_B) +
> > -                            memcg_page_state(memcg, NR_SLAB_UNRECLAIMABLE_B);
> > +                     int idx = i - 1;
> > +
> > +                     size += memcg_page_state(memcg, memory_stats[idx].idx) *
> > +                             memory_stats[idx].ratio;
> >                       seq_buf_printf(&s, "slab %llu\n", size);
> >               }
> >       }
>
> Otherwise the patch looks good to me! Please, feel free to add
> Acked-by: Roman Gushchin <guro@...com>
> after addressing my comments.
>
> Thanks!
> > --
> > 2.11.0
> >



-- 
Yours,
Muchun