Generalize the interface of page space controller.

Generalize the interface of page space controller.

Gather used/capacity/external into SpaceUsage object,
and use it for testing whether GC is needed before or
after an allocation.

This refactor does not affect policy, but prepares for:
1. Replacing promotion failure check/tracking.
2. Better growth control for external allocation.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=34736

[koda, 2014-04-03 17:03:32]

Updated EvaluateGarbageCollection to completely mimic current policy.

[Ivan Posva, 2014-04-04 16:19:10]

Looking at the updated CL now, but had these two comments pending...

-Ivan

https://codereview.chromium.org/220723010/diff/100001/runtime/vm/pages.cc
File runtime/vm/pages.cc (left):

https://codereview.chromium.org/220723010/diff/100001/runtime/vm/pages.cc#old...
runtime/vm/pages.cc:127: capacity_in_words_(0),
I find it a bit surprising and confusing that usage_ is not being setup here.

https://codereview.chromium.org/220723010/diff/100001/runtime/vm/spaces.h
File runtime/vm/spaces.h (right):

https://codereview.chromium.org/220723010/diff/100001/runtime/vm/spaces.h#new...
runtime/vm/spaces.h:14: struct SpaceUsage {
A struct with functions is a class.

[koda, 2014-04-04 16:29:53]

On 2014/04/04 16:19:10, Ivan Posva wrote:
> Looking at the updated CL now, but had these two comments pending...
> 
> -Ivan
> 
> https://codereview.chromium.org/220723010/diff/100001/runtime/vm/pages.cc
> File runtime/vm/pages.cc (left):
> 
>
https://codereview.chromium.org/220723010/diff/100001/runtime/vm/pages.cc#old...
> runtime/vm/pages.cc:127: capacity_in_words_(0),
> I find it a bit surprising and confusing that usage_ is not being setup here.

If another field is added to the struct in the future, I think it's more robust
that the struct itself does the
initialization, rather than having to find all its users.

> 
> https://codereview.chromium.org/220723010/diff/100001/runtime/vm/spaces.h
> File runtime/vm/spaces.h (right):
> 
>
https://codereview.chromium.org/220723010/diff/100001/runtime/vm/spaces.h#new...
> runtime/vm/spaces.h:14: struct SpaceUsage {
> A struct with functions is a class.

I was following the Google style guide, which allows initializers (and
getters/setters):
https://engdoc.corp.google.com/eng/doc/devguide/cpp/styleguide.shtml?cl=head#...

Also, we already have plenty of structs with constructors; 7 of them just in
parser.cc, for instance. Should they all be changed?

[Ivan Posva, 2014-04-04 16:46:24]

Thanks for the explanations.

LGTM

-Ivan

[koda, 2014-04-04 17:46:20]

Committed patchset #9 manually as r34736 (presubmit successful).