Reduce GC from external allocation.

Reduce GC from external allocation.

Before, external allocs artificially reduced new space capacity.
Now, we separately limit on total external size in new space.

Makes scavenges less frequent, while still limiting total footprint.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=34485

[koda, 2014-03-26 00:18:17]

This improves HttpRequest and HttpRequestData benchmarks by 5-8%, and does not
hurt others.

[Anders Johnsen, 2014-03-26 07:09:04]

Yay for speedup! :)

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc
File runtime/vm/heap.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc#newco...
runtime/vm/heap.cc:99: if (new_space_->ExternalInWords() >
FLAG_new_gen_ext_limit * MBInWords) {
DBC:

Just to be sure I get it right: This means that the maximum allocated memory is:
new-gen-size/2 + new-gen-ext-size + old-gen-size?

[koda, 2014-03-26 16:16:28]

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc
File runtime/vm/heap.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc#newco...
runtime/vm/heap.cc:99: if (new_space_->ExternalInWords() >
FLAG_new_gen_ext_limit * MBInWords) {
On 2014/03/26 07:09:04, Anders Johnsen wrote:
> DBC:
> 
> Just to be sure I get it right: This means that the maximum allocated memory
is:
> new-gen-size/2 + new-gen-ext-size + old-gen-size?

Not exactly. The total amount of memory that this heap allocates from the OS is
around new_gen_heap_size + old_gen_heap_size.

The maximum amount of memory that that can actually be used by Dart heap objects
at any moment is slightly less than new_gen_heap_size/2 + old_gen_heap_size.

The total memory footprint that the VM is "aware" of, is new_gen_ext_limit +
new_gen_heap_size + old_gen_heap_size. But there can of course be an arbitrary
amount of user allocations that the user does not tell us about (either because
they are not related to Dart objects, or because they just prefer not to).

[Anders Johnsen, 2014-03-26 18:05:26]

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc
File runtime/vm/heap.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc#newco...
runtime/vm/heap.cc:99: if (new_space_->ExternalInWords() >
FLAG_new_gen_ext_limit * MBInWords) {
On 2014/03/26 16:16:28, koda wrote:
> On 2014/03/26 07:09:04, Anders Johnsen wrote:
> > DBC:
> > 
> > Just to be sure I get it right: This means that the maximum allocated memory
> is:
> > new-gen-size/2 + new-gen-ext-size + old-gen-size?
> 
> Not exactly. The total amount of memory that this heap allocates from the OS
is
> around new_gen_heap_size + old_gen_heap_size.
> 
> The maximum amount of memory that that can actually be used by Dart heap
objects
> at any moment is slightly less than new_gen_heap_size/2 + old_gen_heap_size.
> 
> The total memory footprint that the VM is "aware" of, is new_gen_ext_limit +
> new_gen_heap_size + old_gen_heap_size. But there can of course be an arbitrary
> amount of user allocations that the user does not tell us about (either
because
> they are not related to Dart objects, or because they just prefer not to).

I see. Thanks for explaining!

[Ivan Posva, 2014-03-27 21:18:15]

LGTM -ip

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/dart_api_impl...
File runtime/vm/dart_api_impl_test.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/dart_api_impl...
runtime/vm/dart_api_impl_test.cc:2318: weak1 = Dart_NewWeakPersistentHandle(obj,
Please add comments where you would expect GC, and why as otherwise it is hard
to follow the side-effects.

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc
File runtime/vm/heap.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc#newco...
runtime/vm/heap.cc:99: if (new_space_->ExternalInWords() >
FLAG_new_gen_ext_limit * MBInWords) {
(FLAG_new_gen_ext_limit * MBInWords)

[koda, 2014-03-27 22:11:13]

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/dart_api_impl...
File runtime/vm/dart_api_impl_test.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/dart_api_impl...
runtime/vm/dart_api_impl_test.cc:2318: weak1 = Dart_NewWeakPersistentHandle(obj,
On 2014/03/27 21:18:16, Ivan Posva wrote:
> Please add comments where you would expect GC, and why as otherwise it is hard
> to follow the side-effects.

Done.

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc
File runtime/vm/heap.cc (right):

https://codereview.chromium.org/211593004/diff/90002/runtime/vm/heap.cc#newco...
runtime/vm/heap.cc:99: if (new_space_->ExternalInWords() >
FLAG_new_gen_ext_limit * MBInWords) {
On 2014/03/27 21:18:16, Ivan Posva wrote:
> (FLAG_new_gen_ext_limit * MBInWords)

Done.

[koda, 2014-03-27 22:11:43]

Committed patchset #4 manually as r34485 (presubmit successful).