This keeps fragmentation from delaying
garbage collections (and causing more fragmentation).
Cuts fresh godoc (with indexes) from 261M to 166M (120M live).
Cuts toy wc program from 50M to 8M.
Fixes#647.
R=r, cw
CC=golang-dev
https://golang.org/cl/257041
because free needs to mark the block as freed to
coordinate with the garbage collector.
(in C++ free can blindly put the block on the free list,
no questions asked, so the cache saves some work.)
R=iant
CC=golang-dev
https://golang.org/cl/206069
* specialize sweepspan as sweepspan0 and sweepspan1.
* in sweepspan1, inline "free" to avoid expensive mlookup.
R=iant
CC=golang-dev
https://golang.org/cl/206060
* move memory code into $GOOS-specific directory.
* allow printing of static strings < 256 bytes.
(dynamic strings will bump maxstring as they are allocated.)
* use cgo2c for runtime.mal.
R=r, dho
CC=golang-dev
https://golang.org/cl/186143
