On Mon 28-01-13 18:54:38, Jeff Liu wrote:
> Root memcg with swap cgroup is special since we only do tracking but can
> not set limits against it. In order to facilitate the implementation of
> the coming swap cgroup structures delay allocation mechanism, we can bypass
> the default swap statistics upon the root memcg and figure it out through
> the global stats instead as below:
>
> root_memcg_swap_stat: total_swap_pages - nr_swap_pages - used_swap_pages_of_all_memcgs
How do you protect from races with swap{in,out}? Or they are tolerable?
> memcg_total_swap_stats: root_memcg_swap_stat + other_memcg_swap_stats
I am not sure I understand and if I do then it is not true:
root (swap = 10M, use_hierarchy = 0/1)
\
A (swap = 1M, use_hierarchy = 1)
\
B (swap = 2M)
total for A is 3M regardless of what root has "accounted" while
total for root should be 10 for use_hierarchy = 0 and 13 for the other
case (this is btw. broken in the tree already now because
for_each_mem_cgroup_tree resp. mem_cgroup_iter doesn't honor
use_hierarchy for the root cgroup - this is a separate topic though).
> In this way, we'll return an invalid CSS_ID(generally, it's 0) at swap
> cgroup related tracking infrastructures if only the root memcg is alive.
> That is to say, we have not yet allocate swap cgroup structures.
> As a result, the per pages swapin/swapout stats number agains the root
> memcg shoud be ZERO.
>
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
> CC: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxx>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
> CC: Mel Gorman <mgorman@xxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
> ---
> mm/memcontrol.c | 35 ++++++++++++++++++++++++++++++-----
> 1 file changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 09255ec..afe5e86 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5231,12 +5231,34 @@ 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;
> + long long root_swap_stat = 0;
>
> for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
> - if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
> - continue;
> + long val = 0;
> +
> + if (i != MEM_CGROUP_STAT_SWAP)
> + val = mem_cgroup_read_stat(memcg, i);
> + else {
> + if (!do_swap_account)
> + continue;
> + if (!mem_cgroup_is_root(memcg))
> + val = mem_cgroup_read_stat(memcg, i);
> + else {
> + /*
> + * The corresponding stat number of swap for
> + * root_mem_cgroup is 0 since we don't account
> + * it in any case. Instead, we can fake the
> + * root number via: total_swap_pages -
> + * nr_swap_pages - total_swap_pages_of_all_memcg
> + */
> + for_each_mem_cgroup(mi)
> + val += mem_cgroup_read_stat(mi, i);
> + val = root_swap_stat = (total_swap_pages -
> + nr_swap_pages - val);
> + }
This calls for a helper.
> + }
> 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++)
> @@ -5260,8 +5282,11 @@ static int memcg_stat_show(struct cgroup *cont, struct cftype *cft,
> for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
> long long val = 0;
>
> - if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
> - continue;
> + if (i == MEM_CGROUP_STAT_SWAP) {
> + if (!do_swap_account)
> + continue;
> + val += root_swap_stat * PAGE_SIZE;
> + }
This doesn't seem right because you are adding root swap amount to _all_
groups. This should be done only if (memcg == root_mem_cgroup).
> for_each_mem_cgroup_tree(mi, memcg)
> val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
> seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val);
--
Michal Hocko
SUSE Labs
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