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Date: Wed, 1 May 2024 16:20:45 -0700
From: Roman Gushchin <roman.gushchin@linux.dev>
To: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Muchun Song <muchun.song@linux.dev>,
	Yosry Ahmed <yosryahmed@google.com>,
	"T . J . Mercier" <tjmercier@google.com>, kernel-team@meta.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 4/8] memcg: reduce memory for the lruvec and memcg
 stats
Message-ID: <ZjLOTXEr6XoXf6_g@P9FQF9L96D>
References: <20240501172617.678560-1-shakeel.butt@linux.dev>
 <20240501172617.678560-5-shakeel.butt@linux.dev>
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In-Reply-To: <20240501172617.678560-5-shakeel.butt@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>