On Tue 28-06-11 17:41:50, KAMEZAWA Hiroyuki wrote:
> From 646ca5cd1e1ab0633892b86a1bbb6cf600d79d58 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Date: Tue, 28 Jun 2011 17:09:25 +0900
> Subject: [PATCH 2/3] Fix numa scan information update to be triggered by memory event
>
> commit 889976 adds an numa node round-robin for memcg. But the information
> is updated once per 10sec.
>
> This patch changes the update trigger from jiffies to memcg's event count.
> After this patch, numa scan information will be updated when we see
> 1024 events of pagein/pageout under a memcg.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
See the note about wasted memory for MAX_NUMNODES==1 bellow.
>
> Changelog:
> - simplified
> - removed mutex
> - removed 3% check. To use heuristics, we cannot avoid magic value.
> So, removed heuristics.
> ---
> mm/memcontrol.c | 29 +++++++++++++++++++++++++----
> 1 files changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c624312..3e7d5e6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -108,10 +108,12 @@ enum mem_cgroup_events_index {
> enum mem_cgroup_events_target {
> MEM_CGROUP_TARGET_THRESH,
> MEM_CGROUP_TARGET_SOFTLIMIT,
> + MEM_CGROUP_TARGET_NUMAINFO,
This still wastes sizeof(unsigned long) per CPU space for non NUMA
machines (resp. MAX_NUMNODES==1).
[...]
> @@ -703,6 +709,14 @@ static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
> __mem_cgroup_target_update(mem,
> MEM_CGROUP_TARGET_SOFTLIMIT);
> }
> +#if MAX_NUMNODES > 1
> + if (unlikely(__memcg_event_check(mem,
> + MEM_CGROUP_TARGET_NUMAINFO))) {
> + atomic_inc(&mem->numainfo_events);
> + __mem_cgroup_target_update(mem,
> + MEM_CGROUP_TARGET_NUMAINFO);
> + }
> +#endif
> }
> }
>
> @@ -1582,11 +1596,15 @@ static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *mem,
> static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
> {
> int nid;
> -
> - if (time_after(mem->next_scan_node_update, jiffies))
> + /*
> + * numainfo_events > 0 means there was at least NUMAINFO_EVENTS_TARGET
> + * pagein/pageout changes since the last update.
> + */
> + if (!atomic_read(&mem->numainfo_events))
> + return;
At first I was worried about memory barriers here because
atomic_{set,inc} used for numainfo_events do not imply mem. barriers
but that is not a problem because memcg_check_events will always make
numainfo_events > 0 (even if it doesn't see atomic_set from this
function and we are not interested in the exact value).
> + if (atomic_inc_return(&mem->numainfo_updating) > 1)
> return;
OK, this one should be barrier safe as well as this enforces barrier on
both sides (before and after operation) so the atomic_set shouldn't
break it AFAIU.
>
> - 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];
>
> @@ -1595,6 +1613,9 @@ static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
> if (!test_mem_cgroup_node_reclaimable(mem, nid, false))
> node_clear(nid, mem->scan_nodes);
> }
> +
> + atomic_set(&mem->numainfo_events, 0);
> + atomic_set(&mem->numainfo_updating, 0);
> }
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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