Re: [PATCH v5 7/7] mm: memcontrol: make the slab calculation consistent

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On Wed, Dec 16, 2020 at 7:46 PM Muchun Song <songmuchun@xxxxxxxxxxxxx> 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.
>
> To do this we need some code like below:
>
> 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);
> +       size += memcg_page_state(memcg, memory_stats[i - 1].idx) *
> +               memory_stats[i - 1].ratio;
>
> It requires a series of BUG_ONs or comments to ensure these two
> items are actually adjacent and in the right order. So it would
> probably be easier to implement this using a wrapper that has a
> big switch() for unit conversion.
>
> This would fix the ratio inconsistency and get rid of the order
> guarantee.
>

The commit message is really confusing. It is explaining a situation
which it did not do. I don't see any benefit of mentioning BUG_ONs or
[i-1]s in the message. The patch makes sure that we use the right
ratio for slab. Can you rewrite the commit message and motivate in
just that regard?

> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  mm/memcontrol.c | 105 +++++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 66 insertions(+), 39 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a40797a27f87..eec44918d373 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1511,49 +1511,71 @@ static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
>
>  struct memory_stat {
>         const char *name;
> -       unsigned int ratio;
>         unsigned int idx;
>  };
>
>  static const struct memory_stat memory_stats[] = {
> -       { "anon", PAGE_SIZE, NR_ANON_MAPPED },
> -       { "file", PAGE_SIZE, NR_FILE_PAGES },
> -       { "kernel_stack", 1024, NR_KERNEL_STACK_KB },
> -       { "pagetables", PAGE_SIZE, NR_PAGETABLE },
> -       { "percpu", 1, MEMCG_PERCPU_B },
> -       { "sock", PAGE_SIZE, MEMCG_SOCK },
> -       { "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 },
> +       { "anon",                       NR_ANON_MAPPED                  },
> +       { "file",                       NR_FILE_PAGES                   },
> +       { "kernel_stack",               NR_KERNEL_STACK_KB              },
> +       { "pagetables",                 NR_PAGETABLE                    },
> +       { "percpu",                     MEMCG_PERCPU_B                  },
> +       { "sock",                       MEMCG_SOCK                      },
> +       { "shmem",                      NR_SHMEM                        },
> +       { "file_mapped",                NR_FILE_MAPPED                  },
> +       { "file_dirty",                 NR_FILE_DIRTY                   },
> +       { "file_writeback",             NR_WRITEBACK                    },
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -       { "anon_thp", PAGE_SIZE, NR_ANON_THPS },
> -       { "file_thp", PAGE_SIZE, NR_FILE_THPS },
> -       { "shmem_thp", PAGE_SIZE, NR_SHMEM_THPS },
> +       { "anon_thp",                   NR_ANON_THPS                    },
> +       { "file_thp",                   NR_FILE_THPS                    },
> +       { "shmem_thp",                  NR_SHMEM_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 },
> -
> -       /*
> -        * Note: The slab_reclaimable and slab_unreclaimable must be
> -        * together and slab_reclaimable must be in front.
> -        */
> -       { "slab_reclaimable", 1, NR_SLAB_RECLAIMABLE_B },
> -       { "slab_unreclaimable", 1, NR_SLAB_UNRECLAIMABLE_B },
> +       { "inactive_anon",              NR_INACTIVE_ANON                },
> +       { "active_anon",                NR_ACTIVE_ANON                  },
> +       { "inactive_file",              NR_INACTIVE_FILE                },
> +       { "active_file",                NR_ACTIVE_FILE                  },
> +       { "unevictable",                NR_UNEVICTABLE                  },
> +       { "slab_reclaimable",           NR_SLAB_RECLAIMABLE_B           },
> +       { "slab_unreclaimable",         NR_SLAB_UNRECLAIMABLE_B         },
>
>         /* The memory events */
> -       { "workingset_refault_anon", 1, WORKINGSET_REFAULT_ANON },
> -       { "workingset_refault_file", 1, WORKINGSET_REFAULT_FILE },
> -       { "workingset_activate_anon", 1, WORKINGSET_ACTIVATE_ANON },
> -       { "workingset_activate_file", 1, WORKINGSET_ACTIVATE_FILE },
> -       { "workingset_restore_anon", 1, WORKINGSET_RESTORE_ANON },
> -       { "workingset_restore_file", 1, WORKINGSET_RESTORE_FILE },
> -       { "workingset_nodereclaim", 1, WORKINGSET_NODERECLAIM },
> +       { "workingset_refault_anon",    WORKINGSET_REFAULT_ANON         },
> +       { "workingset_refault_file",    WORKINGSET_REFAULT_FILE         },
> +       { "workingset_activate_anon",   WORKINGSET_ACTIVATE_ANON        },
> +       { "workingset_activate_file",   WORKINGSET_ACTIVATE_FILE        },
> +       { "workingset_restore_anon",    WORKINGSET_RESTORE_ANON         },
> +       { "workingset_restore_file",    WORKINGSET_RESTORE_FILE         },
> +       { "workingset_nodereclaim",     WORKINGSET_NODERECLAIM          },
>  };
>
> +/* Translate stat items to the correct unit for memory.stat output */
> +static int memcg_page_state_unit(int item)
> +{
> +       switch (item) {
> +       case MEMCG_PERCPU_B:
> +       case NR_SLAB_RECLAIMABLE_B:
> +       case NR_SLAB_UNRECLAIMABLE_B:
> +       case WORKINGSET_REFAULT_ANON:
> +       case WORKINGSET_REFAULT_FILE:
> +       case WORKINGSET_ACTIVATE_ANON:
> +       case WORKINGSET_ACTIVATE_FILE:
> +       case WORKINGSET_RESTORE_ANON:
> +       case WORKINGSET_RESTORE_FILE:
> +       case WORKINGSET_NODERECLAIM:
> +               return 1;
> +       case NR_KERNEL_STACK_KB:
> +               return SZ_1K;
> +       default:
> +               return PAGE_SIZE;
> +       }
> +}
> +
> +static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg,
> +                                                   int item)
> +{
> +       return memcg_page_state(memcg, item) * memcg_page_state_unit(item);
> +}
> +
>  static char *memory_stat_format(struct mem_cgroup *memcg)
>  {
>         struct seq_buf s;
> @@ -1577,13 +1599,12 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>         for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
>                 u64 size;
>
> -               size = memcg_page_state(memcg, memory_stats[i].idx);
> -               size *= memory_stats[i].ratio;
> +               size = memcg_page_state_output(memcg, memory_stats[i].idx);
>                 seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size);
>
>                 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);
> +                       size += memcg_page_state_output(memcg,
> +                                                       NR_SLAB_RECLAIMABLE_B);
>                         seq_buf_printf(&s, "slab %llu\n", size);
>                 }
>         }
> @@ -6377,6 +6398,12 @@ static int memory_stat_show(struct seq_file *m, void *v)
>  }
>
>  #ifdef CONFIG_NUMA
> +static inline unsigned long lruvec_page_state_output(struct lruvec *lruvec,
> +                                                    int item)
> +{
> +       return lruvec_page_state(lruvec, item) * memcg_page_state_unit(item);
> +}
> +

No need to have lruvec_page_state_output() separately as there is just
one user. Just inline it.

>  static int memory_numa_stat_show(struct seq_file *m, void *v)
>  {
>         int i;
> @@ -6394,8 +6421,8 @@ static int memory_numa_stat_show(struct seq_file *m, void *v)
>                         struct lruvec *lruvec;
>
>                         lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
> -                       size = lruvec_page_state(lruvec, memory_stats[i].idx);
> -                       size *= memory_stats[i].ratio;
> +                       size = lruvec_page_state_output(lruvec,
> +                                                       memory_stats[i].idx);
>                         seq_printf(m, " N%d=%llu", nid, size);
>                 }
>                 seq_putc(m, '\n');
> --
> 2.11.0
>



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