Re: [PATCHv2] memcg: reclaim memory from node in round-robin

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On Wed, Apr 27, 2011 at 12:51 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> I changed the logic a little and add a filter for skipping nodes.
> With large NUMA, tasks may under cpuset or mempolicy and the usage of memory
> can be unbalanced. So, I think a filter is required.

Thank you.

>
> ==
> 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.
>
>
> From: Ying Han <yinghan@xxxxxxxxxx>
> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Changelog v1->v2:
>  - fixed comments.
>  - added a logic to avoid scanning unused node.
>
> ---
>  include/linux/memcontrol.h |    1
>  mm/memcontrol.c            |   98 ++++++++++++++++++++++++++++++++++++++++++---
>  mm/vmscan.c                |    9 +++-
>  3 files changed, 101 insertions(+), 7 deletions(-)
>
> 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 +237,11 @@ struct mem_cgroup {
>         * reclaimed from.
>         */
>        int last_scanned_child;
> +       int last_scanned_node;
> +#if MAX_NUMNODES > 1
> +       nodemask_t      scan_nodes;
> +       unsigned long   next_scan_node_update;
> +#endif
>        /*
>         * Should the accounting and control be hierarchical, per subtree?
>         */
> @@ -650,18 +655,27 @@ static void mem_cgroup_soft_scan(struct
>        this_cpu_add(mem->stat->events[MEM_CGROUP_EVENTS_SOFT_SCAN], val);
>  }
>
> +static unsigned long
> +mem_cgroup_get_zonestat_node(struct mem_cgroup *mem, int nid, enum lru_list idx)
> +{
> +       struct mem_cgroup_per_zone *mz;
> +       u64 total;
> +       int zid;
> +
> +       for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> +               mz = mem_cgroup_zoneinfo(mem, nid, zid);
> +               total += MEM_CGROUP_ZSTAT(mz, idx);
> +       }
> +       return total;
> +}
>  static unsigned long mem_cgroup_get_local_zonestat(struct mem_cgroup *mem,
>                                        enum lru_list idx)
>  {
> -       int nid, zid;
> -       struct mem_cgroup_per_zone *mz;
> +       int nid;
>        u64 total = 0;
>
>        for_each_online_node(nid)
> -               for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> -                       mz = mem_cgroup_zoneinfo(mem, nid, zid);
> -                       total += MEM_CGROUP_ZSTAT(mz, idx);
> -               }
> +               total += mem_cgroup_get_zonestat_node(mem, nid, idx);
>        return total;
>  }
>
> @@ -1471,6 +1485,77 @@ mem_cgroup_select_victim(struct mem_cgro
>        return ret;
>  }
>
> +#if MAX_NUMNODES > 1
> +
> +/*
> + * Update nodemask always is not very good. Even if we have empty
> + * list, or wrong list here, we can start from some node and traverse all nodes
> + * based on zonelist. So, update the list loosely once in 10 secs.
> + *
> + */
> +static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
> +{
> +       int nid;
> +
> +       if (time_after(mem->next_scan_node_update, jiffies))
> +               return;
> +
> +       mem->next_scan_node_update = jiffies + 10*HZ;
> +       /* make a nodemask where this memcg uses memory from */
> +       mem->scan_nodes = node_states[N_HIGH_MEMORY];
> +
> +       for_each_node_mask(nid, node_states[N_HIGH_MEMORY]) {
> +
> +               if (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_FILE) ||
> +                   mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_FILE))
> +                       continue;
> +
> +               if (total_swap_pages &&
> +                   (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_ANON) ||
> +                    mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_ANON)))
> +                       continue;
> +               node_clear(nid, mem->scan_nodes);
> +       }
> +
> +}
> +
> +/*
> + * Selecting a node where we start reclaim from. Because what we need is just
> + * reducing usage counter, start from anywhere is O,K. 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 means 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;
> +
> +       mem_cgroup_may_update_nodemask(mem);
> +       node = mem->last_scanned_node;
> +
> +       node = next_node(node, mem->scan_nodes);
> +       if (node == MAX_NUMNODES) {
> +               node = first_node(mem->scan_nodes);
> +               if (unlikely(node == MAX_NUMNODES))
> +                       node = numa_node_id();
not sure about this logic, is that possible we reclaim from a node
with all "unreclaimable" pages (based on the
mem_cgroup_may_update_nodemask check).
If i missed anything here, it would be helpful to add comment.

--Ying

> +       }
> +
> +       mem->last_scanned_node = node;
> +       return node;
> +}
> +
> +#else
> +int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
> +{
> +       return 0;
> +}
> +#endif
> +
>  /*
>  * 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
> @@ -4678,6 +4763,7 @@ 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 alloc_pages(), memcg's reclaim
> +        * don't take care of from where we get pages . So, the node where
> +        * we start scan is not needed to be current node.
> +        */
> +       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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