Re: [PATCH] memcg: drain all stocks for the cgroup before readusage

[KAMEZAWA Hiroyuki]

On Thu, 8 Sep 2011 00:33:40 +0300
"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote:

> On Mon, Sep 05, 2011 at 10:16:07AM +0900, Daisuke Nishimura wrote:
> > On Mon, 5 Sep 2011 08:59:13 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > 
> > > On Sun,  4 Sep 2011 04:15:33 +0300
> > > "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote:
> > > 
> > > > From: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
> > > > 
> > > > Currently, mem_cgroup_usage() for non-root cgroup returns usage
> > > > including stocks.
> > > > 
> > > > Let's drain all socks before read resource counter value. It makes
> > > > memory{,.memcg}.usage_in_bytes and memory.stat consistent.
> > > > 
> > > > Signed-off-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> > > 
> > > Hmm. This seems costly to me. 
> > > 
> > > If a user chesk usage_in_bytes in a memcg once per 1sec, 
> > > the kernel will call schedule_work on cpus once per 1sec.
> > > So, IMHO, I don't like this.
> > > 
> > I agree.
> > 
> > We discussed a similar topic on the thread https://lkml.org/lkml/2011/3/18/212.
> > And, we added the memory.txt:
> > ---
> > 5.5 usage_in_bytes
> > 
> > For efficiency, as other kernel components, memory cgroup uses some optimization
> > to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the
> > method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz
> > value for efficient access. (Of course, when necessary, it's synchronized.)
> > If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
> > value in memory.stat(see 5.2).
> > ---
> 
> Agree, thanks.
> 
> Should we have field 'ram' (or 'memory') for rss+cache in memory.stat?
> 

Why do you think so ?

Thanks,
-Kame


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