linux-kernel - Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats

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Date: Mon, 29 Apr 2024 10:35:38 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats

On Fri, Apr 26, 2024 at 5:37 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> At the moment, the amount of memory allocated for stats related structs
> in the mem_cgroup corresponds to the size of enum node_stat_item.
> However not all fields in enum node_stat_item has corresponding memcg
> stats. So, let's use indirection mechanism similar to the one used for
> memcg vmstats management.
>
> For a given x86_64 config, the size of stats with and without patch is:
>
> structs size in bytes         w/o     with
>
> struct lruvec_stats           1128     648
> struct lruvec_stats_percpu     752     432
> struct memcg_vmstats          1832    1352
> struct memcg_vmstats_percpu   1280     960
>
> The memory savings is further compounded by the fact that these structs
> are allocated for each cpu and for each node. To be precise, for each
> memcg the memory saved would be:
>
> Memory saved = ((21 * 3 * NR_NODES) + (21 * 2 * NR_NODS * NR_CPUS) +
>                (21 * 3) + (21 * 2 * NR_CPUS)) * sizeof(long)
>
> Where 21 is the number of fields eliminated.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
>  mm/memcontrol.c | 138 ++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 115 insertions(+), 23 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5e337ed6c6bf..c164bc9b8ed6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -576,35 +576,105 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
>         return mz;
>  }
>
> +/* Subset of node_stat_item for memcg stats */
> +static const unsigned int memcg_node_stat_items[] = {
> +       NR_INACTIVE_ANON,
> +       NR_ACTIVE_ANON,
> +       NR_INACTIVE_FILE,
> +       NR_ACTIVE_FILE,
> +       NR_UNEVICTABLE,
> +       NR_SLAB_RECLAIMABLE_B,
> +       NR_SLAB_UNRECLAIMABLE_B,
> +       WORKINGSET_REFAULT_ANON,
> +       WORKINGSET_REFAULT_FILE,
> +       WORKINGSET_ACTIVATE_ANON,
> +       WORKINGSET_ACTIVATE_FILE,
> +       WORKINGSET_RESTORE_ANON,
> +       WORKINGSET_RESTORE_FILE,
> +       WORKINGSET_NODERECLAIM,
> +       NR_ANON_MAPPED,
> +       NR_FILE_MAPPED,
> +       NR_FILE_PAGES,
> +       NR_FILE_DIRTY,
> +       NR_WRITEBACK,
> +       NR_SHMEM,
> +       NR_SHMEM_THPS,
> +       NR_FILE_THPS,
> +       NR_ANON_THPS,
> +       NR_KERNEL_STACK_KB,
> +       NR_PAGETABLE,
> +       NR_SECONDARY_PAGETABLE,
> +#ifdef CONFIG_SWAP
> +       NR_SWAPCACHE,
> +#endif
> +};
> +
> +static const unsigned int memcg_stat_items[] = {
> +       MEMCG_SWAP,
> +       MEMCG_SOCK,
> +       MEMCG_PERCPU_B,
> +       MEMCG_VMALLOC,
> +       MEMCG_KMEM,
> +       MEMCG_ZSWAP_B,
> +       MEMCG_ZSWAPPED,
> +};

Unsigned for these? All the values are positive now, but I don't think
we'll get a build warning if a negative one ever got added, just a
crash or corruption. BUG_ON in init_memcg_stats if a
memcg_stat_items[i] < 0?