Re: memcg: add mlock statistic in memory.stat

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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 {
> >> > A  A  /* flags for mem_cgroup and file and I/O status */
> >> > A  A  PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
> >> > A  A  PCG_FILE_MAPPED, /* page is accounted as "mapped" */
> >> > + A  PCG_MLOCK, /* page is accounted as "mlock" */
> >> > A  A  /* No lock in page_cgroup */
> >> > A  A  PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
> >> > A  A  __NR_PCG_FLAGS,
> >>
> >> Is this really necessary? A 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 A 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>/? ?

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 ;)

Thanks,
-Kame


 








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