Dave Hansen wrote:
> On Fri, 2009-03-20 at 15:34 -0400, Oren Laadan wrote:
>> 3) In checkpoint, for each task we'll do:
>> if (nsproxy seen first time) {
>> alloc nsproxy_objref
>> for each ns in nsproxy {
>> if (ns seen first time) {
>> alloc ns_objref
>> save state of ns
>> } else {
>> save existing ns_objref
>> }
>> }
>> } else {
>> save existing nsproxy_objref
>> }
>
> The problem with this is that the nsproxy is in no way, shape, or form
> exposed to userspace. It is wholly an internal implementation detail.
>
> Take out all the nsproxy bits you have above, and do this for each task:
>
>> for each ns in nsproxy {
>> if (ns seen first time) {
>> alloc ns_objref
>> save state of ns
>> } else {
>> save existing ns_objref
>> }
>> }
>
> And it will still _function_ *exactly* the same. It won't be quite as
> cache or space compact, but that's fine.
>
> If you're worried about this extra space or cache impact, it can be
> fixed up at restart with:
>
> if (nsproxy_equal(tsk->nsproxy, parent->nsproxy)) {
> get_nsproxy(parent->nsproxy);
> put_nsproxy(tsk->nsproxy);
> tsk->nsproxy = parent->nsproxy;
> }
>
> Voila. It won't be perfect. If the parent doesn't work we could also
> try the siblings.
Yup.
Does that scale well with many (1000's) of tasks ?
(The motivation to expose 'nsproxy_objref' to user space was to allow
user-space to decide on a sequence of clones/unshared that will create
an equivalent process tree with space-efficient nsproxy's).
Perhaps instead of nsproxy_equal() we could use an 'nsproxy_objref'
to know a-priori that it is common, and save the "compare-and-swap"
phase altogether.
Oren.
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