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

[Muchun Song <songmuchun@bytedance.com>]

On Thu, Dec 24, 2020 at 5:21 AM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Wed, Dec 16, 2020 at 7:46 PM Muchun Song <songmuchun@bytedance.com> 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;

Hi Shakeel,

Here is the [i - 1].

> >
> > 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?

Yeah, I need rewrite the commit message to make it more clear.
However, here is a discussion about this. See

    https://lore.kernel.org/patchwork/patch/1348611/

Thanks.

>
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  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
> >



-- 
Yours,
Muchun