linux-kernel - Re: [PATCH 2/3] mm: make workingset detection logic memcg aware

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Date:	Mon, 3 Aug 2015 09:23:58 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: make workingset detection logic memcg aware

On Mon, Aug 03, 2015 at 03:04:22PM +0300, Vladimir Davydov wrote:
> @@ -179,8 +180,9 @@ static void unpack_shadow(void *shadow,
>  	eviction = entry;
>  
>  	*zone = NODE_DATA(nid)->node_zones + zid;
> +	*lruvec = mem_cgroup_page_lruvec(page, *zone);
>  
> -	refault = atomic_long_read(&(*zone)->inactive_age);
> +	refault = atomic_long_read(&(*lruvec)->inactive_age);
>  	mask = ~0UL >> (NODES_SHIFT + ZONES_SHIFT +
>  			RADIX_TREE_EXCEPTIONAL_SHIFT);
>  	/*

You can not compare an eviction shadow entry from one lruvec with the
inactive age of another lruvec. The inactive ages are not related and
might differ significantly: memcgs are created ad hoc, memory hotplug,
page allocator fairness drift. In those cases the result will be pure
noise.

As much as I would like to see a simpler way, I am pessimistic that
there is a way around storing memcg ids in the shadow entries.
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