Re: [RFC] Shared page accounting for memory cgroup

[KAMEZAWA Hiroyuki]

On Mon, 18 Jan 2010 01:00:44 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> On Fri, Jan 8, 2010 at 5:17 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > On Thu, 7 Jan 2010 14:57:36 +0530
> > Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
> >
> >> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-01-07 18:08:00]:
> >>
> >> > On Thu, 7 Jan 2010 17:48:14 +0900
> >> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> >> > > > > "How pages are shared" doesn't show good hints. I don't hear such parameter
> >> > > > > is used in production's resource monitoring software.
> >> > > > >
> >> > > >
> >> > > > You mean "How many pages are shared" are not good hints, please see my
> >> > > > justification above. With Virtualization (look at KSM for example),
> >> > > > shared pages are going to be increasingly important part of the
> >> > > > accounting.
> >> > > >
> >> > >
> >> > > Considering KSM, your cuounting style is tooo bad.
> >> > >
> >> > > You should add
> >> > >
> >> > > Â- MEM_CGROUP_STAT_SHARED_BY_KSM
> >> > > Â- MEM_CGROUP_STAT_FOR_TMPFS/SYSV_IPC_SHMEM
> >> > >
> >>
> >> No.. I am just talking about shared memory being important and shared
> >> accounting being useful, no counters for KSM in particular (in the
> >> memcg context).
> >>
> > Think so ? The number of memcg-private pages is in interest in my point of view.
> >
> > Anyway, I don't change my opinion as "sum of rss" is not necessary to be calculated
> > in the kernel.
> > If you want to provide that in memcg, please add it to global VM as /proc/meminfo.
> >
> > IIUC, KSM/SHMEM has some official method in global VM.
> >
> 
> Kamezawa-San,
> 
> I implemented the same in user space and I get really bad results, here is why
> 
> 1. I need to hold and walk the tasks list in cgroups and extract RSS
> through /proc (results in worse hold times for the fork() scenario you
> menioned)
> 2. The data is highly inconsistent due to the higher margin of error
> in accumulating data which is changing as we run. By the time we total
> and look at the memcg data, the data is stale
> 
> Would you be OK with the patch, if I renamed "shared_usage_in_bytes"
> to "non_private_usage_in_bytes"?
> 
> Given that the stat is user initiated, I don't see your concern w.r.t.
> overhead. Many subsystems like KSM do pay the overhead cost if the
> user really wants the feature or the data. I would be really
> interested in other opinions as well (if people do feel strongly
> against or for the feature)
> 

Please add that featuter to global VM before memcg.
If VM guyes admits its good, I have no objections more.

Thanks,
-Kame




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