(2013/03/12 19:09), Sha Zhengju wrote:
> If memcg is enabled and no non-root memcg exists, all allocated pages
> belong to root_mem_cgroup and go through root memcg statistics routines
> which brings some overheads.
>
> So for the sake of performance, we can give up accounting stats of root
> memcg for MEM_CGROUP_STAT_CACHE/RSS and instead we pay special attention
> to memcg_stat_show() while showing root memcg numbers:
> as we don't account root memcg stats anymore, the root_mem_cgroup->stat
> numbers are actually 0. So we fake these numbers by using stats of global
> state and all other memcg. That is for root memcg:
>
> nr(MEM_CGROUP_STAT_CACHE) = global_page_state(NR_FILE_PAGES) -
> sum_of_all_memcg(MEM_CGROUP_STAT_CACHE);
>
> Rss pages accounting are in the similar way.
>
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 50 ++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 34 insertions(+), 16 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 735cd41..e89204f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -958,26 +958,27 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
> {
> preempt_disable();
>
> - /*
> - * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
> - * counted as CACHE even if it's on ANON LRU.
> - */
> - if (anon)
> - __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
> - nr_pages);
> - else
> - __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
> - nr_pages);
> -
> /* pagein of a big page is an event. So, ignore page size */
> if (nr_pages > 0)
> __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
> - else {
> + else
> __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
> - nr_pages = -nr_pages; /* for event */
> - }
>
> - __this_cpu_add(memcg->stat->nr_page_events, nr_pages);
> + __this_cpu_add(memcg->stat->nr_page_events,
> + nr_pages < 0 ? -nr_pages : nr_pages);
> +
> + if (!mem_cgroup_is_root(memcg)) {
> + /*
> + * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
> + * counted as CACHE even if it's on ANON LRU.
> + */
> + if (anon)
> + __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
> + nr_pages);
> + else
> + __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
> + nr_pages);
> + }
Hmm. I don't like to add this check to this fast path. IIUC, with Costa's patch, root memcg
will not make any charges at all and never call this function. I like his one rather than
this patching.
Thanks,
-Kame
>
> preempt_enable();
> }
> @@ -5445,12 +5446,24 @@ static int memcg_stat_show(struct cgroup *cont, struct cftype *cft,
> struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
> struct mem_cgroup *mi;
> unsigned int i;
> + enum zone_stat_item global_stat[] = {NR_FILE_PAGES, NR_ANON_PAGES};
> + long root_stat[MEM_CGROUP_STAT_NSTATS] = {0};
>
> for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
> + long val = 0;
> +
> if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
> continue;
> +
> + if (mem_cgroup_is_root(memcg) && (i == MEM_CGROUP_STAT_CACHE
> + || i == MEM_CGROUP_STAT_RSS)) {
> + val = global_page_state(global_stat[i]) -
> + mem_cgroup_recursive_stat(memcg, i);
> + root_stat[i] = val = val < 0 ? 0 : val;
> + } else
> + val = mem_cgroup_read_stat(memcg, i);
> seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i],
> - mem_cgroup_read_stat(memcg, i) * PAGE_SIZE);
> + val * PAGE_SIZE);
> }
>
> for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++)
> @@ -5478,6 +5491,11 @@ static int memcg_stat_show(struct cgroup *cont, struct cftype *cft,
> continue;
> for_each_mem_cgroup_tree(mi, memcg)
> val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
> +
> + /* Adding local stats of root memcg */
> + if (mem_cgroup_is_root(memcg))
> + val += root_stat[i] * PAGE_SIZE;
> +
> seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val);
> }
>
>
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