On Tue 25-09-12 12:52:50, Glauber Costa wrote:
> For the root memcg, there is no need to rely on the res_counters.
This is true only if there are no children groups but once there is at
least one we have to move global statistics into root res_counter and
start using it since then. This is a tricky part because it has to be
done atomically so that we do not miss anything.
> The sum of all mem cgroups plus the tasks in root itself, is necessarily
> the amount of memory used for the whole system. Since those figures are
> already kept somewhere anyway, we can just return them here, without too
> much hassle.
>
> The limit can't be set for the root cgroup, so it is left at 0.
You meant RESOURCE_MAX, didn't you?
> Same is
> true for failcnt, because its actual meaning is how many times we failed
> allocations due to the limit being hit. We will fail allocations in the
> root cgroup, but the limit will never the reason.
>
> TODO includes figuring out what to do with the soft limit and max_usage.
> Comments and suggestions appreciated.
>
> Signed-off-by: Glauber Costa <[email protected]>
> CC: Michal Hocko <[email protected]>
> CC: Kamezawa Hiroyuki <[email protected]>
> CC: Johannes Weiner <[email protected]>
> CC: Mel Gorman <[email protected]>
> CC: Andrew Morton <[email protected]>
> ---
> mm/memcontrol.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 82c5b8f..bac398b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4506,6 +4506,45 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
> return val << PAGE_SHIFT;
> }
>
> +static u64 mem_cgroup_read_root(struct mem_cgroup *memcg, enum res_type type, int name)
> +{
> + struct sysinfo i;
> + unsigned long pages[NR_LRU_LISTS];
> + int lru;
> +
> + si_meminfo(&i);
> + si_swapinfo(&i);
> +
> + if (name == RES_LIMIT)
> + return RESOURCE_MAX;
> + if (name == RES_SOFT_LIMIT)
> + return 0;
> + if (name == RES_FAILCNT)
> + return 0;
> + if (name == RES_MAX_USAGE)
> + return 0;
> +
> + if (WARN_ON_ONCE(name != RES_USAGE))
> + return 0;
> +
> + for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
> + pages[lru] = global_page_state(NR_LRU_BASE + lru);
> +
> + switch (type) {
> + case _MEM:
> + return pages[LRU_ACTIVE_ANON] + pages[LRU_ACTIVE_FILE] +
> + pages[LRU_INACTIVE_ANON] + pages[LRU_INACTIVE_FILE];
> + case _MEMSWAP:
> + return pages[LRU_ACTIVE_ANON] + pages[LRU_ACTIVE_FILE] +
> + pages[LRU_INACTIVE_ANON] + pages[LRU_INACTIVE_FILE] +
> + i.totalswap - i.freeswap;
> + case _KMEM:
> + return 0;
> + default:
> + BUG();
> + };
> +}
> +
> static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
> struct file *file, char __user *buf,
> size_t nbytes, loff_t *ppos)
> @@ -4522,6 +4561,11 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
> if (!do_swap_account && type == _MEMSWAP)
> return -EOPNOTSUPP;
>
> + if (mem_cgroup_is_root(memcg)) {
> + val = mem_cgroup_read_root(memcg, type, name);
> + goto root_bypass;
> + }
> +
> switch (type) {
> case _MEM:
> if (name == RES_USAGE)
> @@ -4542,6 +4586,7 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
> BUG();
> }
>
> +root_bypass:
> len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
> return simple_read_from_buffer(buf, nbytes, ppos, str, len);
> }
> --
> 1.7.11.4
>
> --
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--
Michal Hocko
SUSE Labs
On 10/01/2012 09:00 PM, Michal Hocko wrote:
> On Tue 25-09-12 12:52:50, Glauber Costa wrote:
>> > For the root memcg, there is no need to rely on the res_counters.
> This is true only if there are no children groups but once there is at
> least one we have to move global statistics into root res_counter and
> start using it since then. This is a tricky part because it has to be
> done atomically so that we do not miss anything.
>
Why can't we shortcut it all the time?
It makes a lot of sense to use the root cgroup as the sum of everything,
IOW, global counters. Otherwise you are left in a situation where you
had global statistics, and all of a sudden, when a group is created, you
start having just a subset of that, excluding the tasks in root.
If we can always assume root will have the sum of *all* tasks, including
the ones in root, we should never need to rely on root res_counters.
On Tue 02-10-12 13:15:43, Glauber Costa wrote:
> On 10/01/2012 09:00 PM, Michal Hocko wrote:
> > On Tue 25-09-12 12:52:50, Glauber Costa wrote:
> >> > For the root memcg, there is no need to rely on the res_counters.
> > This is true only if there are no children groups but once there is at
> > least one we have to move global statistics into root res_counter and
> > start using it since then. This is a tricky part because it has to be
> > done atomically so that we do not miss anything.
> >
> Why can't we shortcut it all the time?
Because it has its own tasks and we are still not at use_hierarchy := 1
> It makes a lot of sense to use the root cgroup as the sum of everything,
> IOW, global counters. Otherwise you are left in a situation where you
> had global statistics, and all of a sudden, when a group is created, you
> start having just a subset of that, excluding the tasks in root.
Yes because if there are no other tasks then, well, global == root. Once
you have more groups (with tasks of course) then it depends on our
favorite use_hierarchy buddy.
> If we can always assume root will have the sum of *all* tasks, including
> the ones in root, we should never need to rely on root res_counters.
but we are not there yet.
--
Michal Hocko
SUSE Labs