On Wed, Sep 26, 2012 at 12:53:21PM +0400, Glauber Costa wrote:

On 09/26/2012 01:02 AM, Andrew Morton wrote:

quoted

quoted

nomemcg  : memcg compile disabled.

quoted

base     : memcg enabled, patch not applied.
bypassed : memcg enabled, with patch applied.

                base    bypassed
User          109.12      105.64
System       1646.84     1597.98
Elapsed       229.56      215.76

             nomemcg    bypassed
User          104.35      105.64
System       1578.19     1597.98
Elapsed       212.33      215.76

So as one can see, the difference between base and nomemcg in terms
of both system time and elapsed time is quite drastic, and consistent
with the figures shown by Mel Gorman in the Kernel summit. This is a
~ 7 % drop in performance, just by having memcg enabled. memcg functions
appear heavily in the profiles, even if all tasks lives in the root
memcg.

With bypassed kernel, we drop this down to 1.5 %, which starts to fall
in the acceptable range. More investigation is needed to see if we can
claim that last percent back, but I believe at last part of it should
be.

Well that's encouraging.  I wonder how many users will actually benefit
from this - did I hear that major distros are now using memcg in some
system-infrastructure-style code?

If they do, they actually be come "users of memcg". This here is aimed
at non-users of memcg, which given all the whining about it, it seems to
be plenty.

Also, I noticed, for instance, that libvirt is now creating memcg
hierarchies for lxc and qemu as placeholders, before you actually create
any vm or container.

This is mostly just lazyness on our part. There's no technical reason
why we can't delay creating our intermediate cgroups until we actually
have a VM ready to start, it was just simpler to create them when we
started the main daemon.


Daniel
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