[golang-dev] Re: code review 6655045: cmd/5l: reorder some struct fields to reduce memory con... (issue 6655045)

As I didn't suspect gc would use much memory, I haven't looked at gc.

But I suspect there are similar saving in gc.

The same reordering is applicable to gc, but i think gc orders fields for
better documentations (group related fields together), and the space
saving won't be big if i can't reorder the fields freely.

Russ said that gc put every number (even 0 is) as bigint/bigfloat, and
removing
that could bring us big space savings. Also, he said that we could reuse
used
number (or cache small frequently used numbers, say -1, 0, 1-100, 128, 256,
etc
in an array).

As far as I remember, the largest memory usage when compiling the
dreadful output of test/rotate.go was essentially in Nodes. It's not
clear what we can do for that.

Rémy.

Yeah, true.

By freely reordering struct Node, I can make the 6g's maximum RSS
smaller by 1.43% (from 5357168 KiB to 5281024 KiB, -76144 KiB).

After reordering struct Sym, RSS go down by 3776 KiB (to 5277248 KiB).

After reordering struct Type, RSS go down by 9168 KiB (to 5268080 KiB).

To see the maximum RSS saved this way, I added #pragma pack to gc/go.h,
and the RSS is now 5198800 KiB (down by 158368 KiB, a merely 3%).

No big improvements (and doing this will severely affect code documentation
quality), so maybe we need to use different type of Node struct for
different
kinds of node (which is a pretty big task).

5.3Gb to compile! That is getting into Firefox territory.
http://www.phoronix.com/scan.php?page=news_item&px=MTA3MTQ

That's the very reason that test is not enabled by default, or
all the builders will blow up. :-)

*** Submitted as
http://code.google.com/p/go/source/detail?r=1baa80f7f4a4 ***

cmd/5l: reorder some struct fields to reduce memory consumption
Valgrind Massif result when linking godoc:
On amd64:
old new -/+
mem_heap_B 185844612 175358047 -5.7%
mem_heap_extra_B 773404 773137 -0.0%

On 386/ARM:
old new -/+
mem_heap_B 141775701 131289941 -7.4%
mem_heap_extra_B 737011 736955 -0.0%

R=golang-dev, r, dave
CC=golang-dev
http://codereview.appspot.com/6655045


http://codereview.appspot.com/6655045/