[Devel] Re: [PATCH] Simplify memory controller and resource counter I/O

[Paul Menage]

On 10/4/07, Balbir Singh <balbir at linux.vnet.ibm.com> wrote:
> Paul Menage wrote:
> > On 10/4/07, Balbir Singh <balbir at linux.vnet.ibm.com> wrote:
> >> Forbidding writing to the root resource counter is a policy decision
> >> I am unable to make up my mind about. It sounds right, but unless
> >> we have a notion of unlimited resources, I am a bit concerned about
> >> taking away this flexibility.
> >
> > One big reason for doing this is to make virtualization easier - if
> > you expect not to be able to write to your root cgroup's limits files,
> > then it's easier to make them non-writeable for a virtual server.
> >
>
> Can't we handle that through file system permissions? virtual servers
> will not run as root

They'll probably run as root in their own user namespace if at all.
But that's the point - if userspace in general expects root cgroup
limits to not be writeable (the same way that root cpusets
cpus/mems_allowed files aren't writeable) then virtual servers will
break less.

>
> But system administrators deal with memory in MB and GB. When you go
> to buy memory, you don't specify, I need 1 << 30 or 2^30 bytes of
> memory :-). Most administrators track their memory using these
> quantifiers.

OK, so maybe we should just fold a call to memparse() into
cgroup_write_uint? Then we could use the plain write_uint() method in
the control file?

>
> >> Do read_uint() and write_uint(), just read and write unsigned
> >> integers?
> >
> > Correct.
> >
>
> Oops.. that would be problem, what if I wanted to set my limit to
> unsigned long long max?

Sorry, I wasn't getting your point about the sizing. No, they're u64
values. (And I guess could be changed to unsigned long long if people
preferred).

Paul
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