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

From: Shakeel Butt
Date: Wed Dec 23 2020 - 16:22:49 EST

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
>