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SubjectRe: [PATCHv3] memcg: reclaim memory from node in round-robin
On Thu, 28 Apr 2011 09:35:13 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> 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
^^^^^
cache
> 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. With using cpuset's spread memory feature, this will work very well.
>
> But yes, better algorithm is appreciated.
>
> From: Ying Han <yinghan@google.com>
> Signed-off-by: Ying Han <yinghan@google.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> Changelog v2->v3
> - added comments for why we need sanity check.
>
> Changelog v1->v2:
> - fixed comments.
> - added a logic to avoid scanning unused node.
>
> ---
> include/linux/memcontrol.h | 1
> mm/memcontrol.c | 102 ++++++++++++++++++++++++++++++++++++++++++---
> mm/vmscan.c | 9 +++
> 3 files changed, 105 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 +1485,81 @@ 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;
> +
Shouldn't it be time_before() or time_after(jiffies, next_scan_node_update) ?

Looks good to me, otherwise.

Thanks,
Daisuke Nishimura.

> + 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);
> + /*
> + * We call this when we hit limit, not when pages are added to LRU.
> + * No LRU may hold pages because all pages are UNEVICTABLE or
> + * memcg is too small and all pages are not on LRU. In that case,
> + * we use curret node.
> + */
> + if (unlikely(node == MAX_NUMNODES))
> + node = numa_node_id();
> +
> + 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 +4767,7 @@ 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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