Re: [PATCH 1/2] rcfs core patch

[Herbert Poetzl]

On Fri, Mar 09, 2007 at 11:44:22PM +0530, Srivatsa Vaddagiri wrote:
> On Fri, Mar 09, 2007 at 01:48:16AM +0100, Herbert Poetzl wrote:
> > > There have been various projects attempting to provide resource
> > > management support in Linux, including CKRM/Resource Groups and UBC.

> > let me note here, once again, that you forgot Linux-VServer
> > which does quite non-intrusive resource management ...

> Sorry, not intentionally. Maybe it slipped because I haven't
> seen much res mgmt related patches from Linux Vserver on 
> lkml recently.

mainly because I got the impression that we planned
to work on the various spaces first, and handle things
like resource management later .. but it seems that
resource management is now in focus, while the spaces
got somewhat delayed ...

> Note that I -did- talk about VServer at one point in past
> (http://lkml.org/lkml/2006/06/15/112)!

noted and appreciated (although this was about CPU
resources, which IMHO is a special resource like
the networking, as you are mostly interested in
'bandwidth' limitations there, not in resource
limits per se (and of course, it wasn't even cited
correctly, as it is Linux-VServer not vserver ...)

> > the basic 'context' (pid space) is the grouping mechanism
> > we use for resource management too

> so tasks sharing the same nsproxy->pid_ns is the fundamental
> unit of resource management (as far as vserver/container goes)?

we currently have a 'process' context, which holds
the administrative data (capabilities and flags) and
the resource accounting and limits, which basically
contains the pid namespace, so yes and no

it contains a reference to the 'main' nsproxy, which
is used to copy spaces from when you enter the guest
(or some set of spaces), and it defines the unit we
consider a process container

> > > As you know, the introduction of 'struct container' was objected
> > > to and was felt redundant as a means to group tasks. Thats where
> > > I took a shot at converting over Paul Menage's patch to avoid
> > > 'struct container' abstraction and insead work with 'struct
> > > nsproxy'.
> > 
> > which IMHO isn't a step in the right direction, as
> > you will need to handle different nsproxies within
> > the same 'resource container' (see previous email)
> 
> Isn't that made simple because of the fact that we have pointers to
> namespace objects (and not actual objects themselves) in nsproxy?
> 
> I mean, all that is required to manage multiple nsproxy's
> is to have the pointer to the same resource object in all of them.
> 
> In system call terms, if someone does a unshare of uts namespace, 
> he will get into a new nsproxy object sure (which has a pointer to the
> new uts namespace) but the new nsproxy object will still be pointing
> to the old resource controlling objects.

yes, that is why I agreed, that the container (or
resource limit/accounting/controlling object) can
be seen as space too (and handled like that)

> > > When we support task movement across resource classes, we need to
> > > find a nsproxy which has the right combination of resource classes
> > > that the task's nsproxy can be hooked to.
> > 
> > no, not necessarily, we can simply create a new one
> > and give it the proper resource or whatever-spaces
> 
> That would be the simplest, agreeably. But not optimal in terms of
> storage?
> 
> Pls note that task-movement can be not-so-infrequent 
> (in other words, frequent) in context of non-container workload 
> management.

not only there, also with solutions like Linux-VServer
(it is quite common to enter guests or subsets of the
space mix assigned)

> > why is the filesystem approach so favored for this
> > kind of manipulations?
> > 
> > IMHO it is one of the worst interfaces I can imagine
> > (to move tasks between spaces and/or assign resources)
> > but yes, I'm aware that filesystems are 'in' nowadays
> 
> Ease of use maybe. Scripts can be more readily used with a fs-based
> interface.

correct, but what about security and/or atomicity?
i.e. how to assure that some action really was 
taken and/or how to wait for completion?

sure, all this _can_ be done, no doubt, but it
is much harder to do with a fs based interface than
with e.g. a syscall interface ...

> -- 
> Regards,
> vatsa
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