Re: [Devel] Re: BC: resource beancounters (v2)

From: Kir Kolyshkin
Date: Mon Aug 28 2006 - 13:39:42 EST


Rohit Seth wrote:
On Sat, 2006-08-26 at 17:37 +0100, Alan Cox wrote:
Ar Gwe, 2006-08-25 am 19:15 -0700, ysgrifennodd Rohit Seth:
Yes, sharing of pages across different containers/managers will be a
problem. Why not just disallow that scenario (that is what fake nodes
proposal would also end up doing).
Because it destroys the entire point of using containers instead of
something like Xen - which is sharing. Also at the point I am using
beancounters per user I don't want glibc per use, libX11 per use glib
per use gtk per user etc..



I'm not saying per use glibc etc. That will indeed be useless and bring
it to virtualization world. Just like fake node, one should be allowed
to use pages that are already in (for example) page cache- so that you
don't end up duplicating all shared stuff. But as far as charging is
concerned, charge it to container who either got the page in page cache
OR if FS based semantics exist then charge it to the container where the
file belongs. What I was suggesting is to not charge a page to
different counters.

Consider the following simple scenario: there are 50 containers (numbered, say, 1 to 50) all sharing a single installation of Fedora Core 5. They all run sshd, apache, syslogd, crond and some other stuff like that. This is actually quite a real scenario.

In the world that you propose the container which was unlucky to start first (probably the one with ID of either 1 or 50) will be charged for all the memory, and all the
others will have most of their memory for free. And in such a world per-container memory accounting or limiting is just not possible.
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