Re: memcg: add mlock statistic in memory.stat

[Ying Han <yinghan@google.com>]

On Wed, Jan 11, 2012 at 7:21 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Wed, 11 Jan 2012 16:50:09 -0800
> Ying Han <yinghan@google.com> wrote:
>
>> On Wed, Jan 11, 2012 at 3:59 PM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > On Wed, 11 Jan 2012 15:17:42 -0800 (PST)
>> > Hugh Dickins <hughd@google.com> wrote:
>> >
>> >> On Wed, 11 Jan 2012, Ying Han wrote:
>> >>
>> >> > We have the nr_mlock stat both in meminfo as well as vmstat system wide, this
>> >> > patch adds the mlock field into per-memcg memory stat. The stat itself enhances
>> >> > the metrics exported by memcg, especially is used together with "uneivctable"
>> >> > lru stat.
>> >> >
>> >> > --- a/include/linux/page_cgroup.h
>> >> > +++ b/include/linux/page_cgroup.h
>> >> > @@ -10,6 +10,7 @@ enum {
>> >> >     /* flags for mem_cgroup and file and I/O status */
>> >> >     PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
>> >> >     PCG_FILE_MAPPED, /* page is accounted as "mapped" */
>> >> > +   PCG_MLOCK, /* page is accounted as "mlock" */
>> >> >     /* No lock in page_cgroup */
>> >> >     PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
>> >> >     __NR_PCG_FLAGS,
>> >>
>> >> Is this really necessary?  KAMEZAWA-san is engaged in trying to reduce
>> >> the number of PageCgroup flags, and I expect that in due course we shall
>> >> want to merge them in with Page flags, so adding more is unwelcome.
>> >> I'd  have thought that with memcg_ hooks in the right places,
>> >> a separate flag would not be necessary?
>> >>
>> >
>> > Please don't ;)
>> >
>> > NR_UNEIVCTABLE_LRU is not enough ?
>>
>> Seems not.
>>
>> The unevictable lru includes more than mlock()'d pages ( SHM_LOCK'd
>> etc). There are use cases where we like to know the mlock-ed size
>> per-cgroup. We used to archived that in fake-numa based container by
>> reading the value from per-node meminfo, however we miss that
>> information in memcg. What do you think?
>>
>
> Hm. The # of mlocked pages can be got sum of /proc/<pid>/? ?

That is tough. Then we have to do the calculation by adding up all the
pids within a cgroup.

> BTW, Roughly..
>
> (inactive_anon + active_anon) - rss = # of unlocked shm.
>
> cache - (inactive_file + active_file) = total # of shm
>
> Then,
>
> (cache -  (inactive_file + active_file)) - ((inactive_anon + active_anon) - rss)
> = cache + rss - (sum of inactive/actige lru)
> = locked shm.
>
> Hm, but this works only when unmapped swapcache is  small ;)

We might be getting a rough number. But we have use cases relying on
more accurate output. Thoughts?

Thanks

--Ying

>
> Thanks,
> -Kame
>
>
>
>
>
>
>
>
>
>
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>