On Mon, Dec 20, 2021 at 04:56:34PM +0800, Muchun Song wrote:
> The list_lru uses an array (list_lru_memcg->lru) to store pointers
> which point to the list_lru_one. And the array is per memcg per node.
> Therefore, the size of the arrays will be 10K * number_of_node * 8 (
> a pointer size on 64 bits system) when we run 10k containers in the
> system. The memory consumption of the arrays becomes significant. The
> more numa node, the more memory it consumes.
>
> I have done a simple test, which creates 10K memcg and mount point
> each in a two-node system. The memory consumption of the list_lru
> will be 24464MB. After converting the array from per memcg per node
> to per memcg, the memory consumption is going to be 21957MB. It is
> reduces by 2.5GB. In our AMD servers with 8 numa nodes in those
> sysuem, the memory consumption could be more significant. The savings
> come from the list_lru_one heads, that it also simplifies the
> alloc/dealloc path.
>
> The new scheme looks like the following.
>
> +----------+ mlrus +----------------+ mlru +----------------------+
> | list_lru +---------->| list_lru_memcg +--------->| list_lru_per_memcg |
> +----------+ +----------------+ +----------------------+
> | list_lru_per_memcg |
> +----------------------+
> | ... |
> +--------------+ node +----------------------+
> | list_lru_one |<----------+ list_lru_per_memcg |
> +--------------+ +----------------------+
> | list_lru_one |
> +--------------+
> | ... |
> +--------------+
> | list_lru_one |
> +--------------+
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
As much as I like the code changes (there is indeed a significant simplification!),
I don't like the commit message and title, because I wasn't able to understand
what the patch is doing and some parts look simply questionable. Overall it
sounds like you reduce the number of list_lru_one structures, which is not true.
How about something like this?
--
mm: list_lru: transpose the array of per-node per-memcg lru lists
The current scheme of maintaining per-node per-memcg lru lists looks like:
struct list_lru {
struct list_lru_node *node; (for each node)
struct list_lru_memcg *memcg_lrus;
struct list_lru_one *lru[]; (for each memcg)
}
By effectively transposing the two-dimension array of list_lru_one's structures
(per-node per-memcg => per-memcg per-node) it's possible to save some memory
and simplify alloc/dealloc paths. The new scheme looks like:
struct list_lru {
struct list_lru_memcg *mlrus;
struct list_lru_per_memcg *mlru[]; (for each memcg)
struct list_lru_one node[0]; (for each node)
}
Memory savings are coming from having fewer list_lru_memcg structures, which
contain an extra struct rcu_head to handle the destruction process.
--
But what worries me is that memory savings numbers you posted don't do up.
In theory we can save
16 (size of struct rcu_head) * 10000 (number of cgroups) * 2 (number of numa nodes) = 320k
per slab cache. Did you have a ton of mount points? Otherwise I don't understand
where these 2.5Gb are coming from.
Thanks!
