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

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Message-ID: <2aea9490-99aa-4e55-e7ca-22b695eee1da@suse.cz>
Date:	Thu, 16 Jun 2016 17:06:46 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>
Cc:	Rik van Riel <riel@...riel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones
 to nodes

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@...hsingularity.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];
>  }
>