Re: [PATCH v4 4/8] memcg: reduce memory for the lruvec and memcg stats

[Roman Gushchin <roman.gushchin@linux.dev>]

On Wed, May 01, 2024 at 10:26:13AM -0700, Shakeel Butt 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 have 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_NODES * 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@linux.dev>

Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>