Re: [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones to nodes

Vlastimil Babka
2016-06-16T15:06:52Z

On 06/09/2016 08:04 PM, Mel Gorman wrote:
> Memcg was broken by the move of all LRUs to nodes because it is tracking
> limits on a per-zone basis while receiving reclaim requests on a per-node
> basis. This patch moves limit enforcement to the nodes. Technically, all
> the variable names should also change but people are already familiar by
> the meaning of "mz" even if "mn" would be a more appropriate name now.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

Didn't spot bugs, but I'm not that familiar with memcg. Noticed some
things below to further optimize/cleanup.

[...]

> @@ -323,13 +319,10 @@ EXPORT_SYMBOL(memcg_kmem_enabled_key);
>
> #endif /* !CONFIG_SLOB */
>
> -static struct mem_cgroup_per_zone *
> -mem_cgroup_zone_zoneinfo(struct mem_cgroup *memcg, struct zone *zone)
> +static struct mem_cgroup_per_node *
> +mem_cgroup_nodeinfo(struct mem_cgroup *memcg, pg_data_t *pgdat)
> {
> - int nid = zone_to_nid(zone);
> - int zid = zone_idx(zone);
> -
> - return &memcg->nodeinfo[nid]->zoneinfo[zid];
> + return memcg->nodeinfo[pgdat->node_id];

I've noticed most callers pass NODE_DATA(nid) as second parameter, which
is quite wasteful to just obtain back the node_id (I doubt the compiler
can know that they will be the same?). So it would be more efficient to
use nid instead of pg_data_t pointer in the signature.

> }
>
> /**
> @@ -383,37 +376,35 @@ ino_t page_cgroup_ino(struct page *page)
> return ino;
> }
>
> -static struct mem_cgroup_per_zone *
> +static struct mem_cgroup_per_node *
> mem_cgroup_page_zoneinfo(struct mem_cgroup *memcg, struct page *page)

This could be renamed to _nodeinfo()?

> {
> int nid = page_to_nid(page);
> - int zid = page_zonenum(page);
>
> - return &memcg->nodeinfo[nid]->zoneinfo[zid];
> + return memcg->nodeinfo[nid];
> }
>