code review 4118042: runtime: simpler heap map, memory allocation

runtime: simpler heap map, memory allocation

The old heap maps used a multilevel table, but that
was overkill: there are only 1M entries on a 32-bit
machine and we can arrange to use a dense address
range on a 64-bit machine.

The heap map is in bss.  The assumption is that if
we don't touch the pages they won't be mapped in.

Also moved some duplicated memory allocation
code out of the OS-specific files.

[rsc, 2011-01-28 19:42:05]

Hello r (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[r, 2011-01-28 19:56:15]

LGTM

it does seem better

http://codereview.appspot.com/4118042/diff/11001/src/pkg/runtime/malloc.goc
File src/pkg/runtime/malloc.goc (right):

http://codereview.appspot.com/4118042/diff/11001/src/pkg/runtime/malloc.goc#n...
src/pkg/runtime/malloc.goc:262: // possible let's try to get one starting at
0x000000f800000000.
the "if possible" implies another attempt on failure, but you only try once.

http://codereview.appspot.com/4118042/diff/11001/src/pkg/runtime/malloc.goc#n...
src/pkg/runtime/malloc.goc:275: // that matched a memory address.
nice

[rsc, 2011-01-28 19:58:27]

>
http://codereview.appspot.com/4118042/diff/11001/src/pkg/runtime/malloc.goc#n...
> src/pkg/runtime/malloc.goc:262: // possible let's try to get one
> starting at 0x000000f800000000.
> the "if possible" implies another attempt on failure, but you only try
> once.

SysReserve uses the address as a hint.
it can return something else.  will fix the comment.

[rsc, 2011-01-28 20:03:30]

*** Submitted as http://code.google.com/p/go/source/detail?r=dba56641aa19 ***

runtime: simpler heap map, memory allocation

The old heap maps used a multilevel table, but that
was overkill: there are only 1M entries on a 32-bit
machine and we can arrange to use a dense address
range on a 64-bit machine.

The heap map is in bss.  The assumption is that if
we don't touch the pages they won't be mapped in.

Also moved some duplicated memory allocation
code out of the OS-specific files.

R=r
CC=golang-dev
http://codereview.appspot.com/4118042