Re: [PATCH] memcg: reclaim memory from nodes in round robin

[Ying Han]

On Tue, Apr 26, 2011 at 7:57 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> Now, memory cgroup's direct reclaim frees memory from the current node.
> But this has some troubles. In usual, when a set of threads works in
> cooperative way, they are tend to on the same node. So, if they hit
> limits under memcg, it will reclaim memory from themselves, it may be
> active working set.
>
> For example, assume 2 node system which has Node 0 and Node 1
> and a memcg which has 1G limit. After some work, file cacne remains and
> and usages are
>   Node 0:  1M
>   Node 1:  998M.
>
> and run an application on Node 0, it will eats its foot before freeing
> unnecessary file caches.
>
> This patch adds round-robin for NUMA and adds equal pressure to each
> node. When using cpuset's spread memory feature, this will work very well.
>
> But yes, better algorithm is appreciated.
>
> From: Ying Han <yinghan@xxxxxxxxxx>
> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
>  include/linux/memcontrol.h |    1 +
>  mm/memcontrol.c            |   25 +++++++++++++++++++++++++
>  mm/vmscan.c                |    9 ++++++++-
>  3 files changed, 34 insertions(+), 1 deletion(-)
>
> Index: memcg/include/linux/memcontrol.h
> ===================================================================
> --- memcg.orig/include/linux/memcontrol.h
> +++ memcg/include/linux/memcontrol.h
> @@ -108,6 +108,7 @@ extern void mem_cgroup_end_migration(str
>  */
>  int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg);
>  int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg);
> +int mem_cgroup_select_victim_node(struct mem_cgroup *memcg);
>  unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
>                                       struct zone *zone,
>                                       enum lru_list lru);
> Index: memcg/mm/memcontrol.c
> ===================================================================
> --- memcg.orig/mm/memcontrol.c
> +++ memcg/mm/memcontrol.c
> @@ -237,6 +237,7 @@ struct mem_cgroup {
>         * reclaimed from.
>         */
>        int last_scanned_child;
> +       int last_scanned_node;
>        /*
>         * Should the accounting and control be hierarchical, per subtree?
>         */
> @@ -1472,6 +1473,29 @@ mem_cgroup_select_victim(struct mem_cgro
>  }
>
>  /*
> + * Selecting a node where we start reclaim from. Because what we need is just
> + * reducing usage counter, start from anywhere is O,K. When considering
> + * memory reclaim from current node, there are pros. and cons.
> + * Freeing memory from current node means freeing memory from a node which
> + * we'll use or we've used. So, it may make LRU bad. And if several threads
> + * hit limits, it will see a contention on a node. But freeing from remote
> + * node mean more costs for memory reclaim because of memory latency.
> + *
> + * Now, we use round-robin. Better algorithm is welcomed.
> + */
> +int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
> +{
> +       int node;
> +
> +       node = next_node(mem->last_scanned_node, node_states[N_HIGH_MEMORY]);
> +       if (node == MAX_NUMNODES)
> +               node = first_node(node_states[N_HIGH_MEMORY]);
> +
> +       mem->last_scanned_node = node;
> +       return node;
> +}
> +
> +/*
>  * Scan the hierarchy if needed to reclaim memory. We remember the last child
>  * we reclaimed from, so that we don't end up penalizing one child extensively
>  * based on its position in the children list.
> @@ -4678,6 +4702,7 @@ mem_cgroup_create(struct cgroup_subsys *
>                res_counter_init(&mem->memsw, NULL);
>        }
>        mem->last_scanned_child = 0;
> +       mem->last_scanned_node = MAX_NUMNODES;
>        INIT_LIST_HEAD(&mem->oom_notify);
>
>        if (parent)
> Index: memcg/mm/vmscan.c
> ===================================================================
> --- memcg.orig/mm/vmscan.c
> +++ memcg/mm/vmscan.c
> @@ -2198,6 +2198,7 @@ unsigned long try_to_free_mem_cgroup_pag
>  {
>        struct zonelist *zonelist;
>        unsigned long nr_reclaimed;
> +       int nid;
>        struct scan_control sc = {
>                .may_writepage = !laptop_mode,
>                .may_unmap = 1,
> @@ -2208,10 +2209,16 @@ unsigned long try_to_free_mem_cgroup_pag
>                .mem_cgroup = mem_cont,
>                .nodemask = NULL, /* we don't care the placement */
>        };
> +       /*
> +        * Unlike direct reclaim via allo_pages(), memcg's reclaim
> +        * don't take care from where we get free resouce. So, the node where
> +        * we need to start scan is not need to be current node.
> +        */
Sorry, some typos. alloc_pages() instead of alloc_pages(). And "free resource".

--Ying
> +       nid = mem_cgroup_select_victim_node(mem_cont);
>
>        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
>                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
> -       zonelist = NODE_DATA(numa_node_id())->node_zonelists;
> +       zonelist = NODE_DATA(nid)->node_zonelists;
>
>        trace_mm_vmscan_memcg_reclaim_begin(0,
>                                            sc.may_writepage,
>
>
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