runtime: expand comment on work.spans

Change-Id: I4b8a6f5d9bc5aba16026d17f99f3512dacde8d2d
Reviewed-on: https://go-review.googlesource.com/30534
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index f44a4fbb0382110839e522523119835a2fe7d384..6be1ffda99410df72892f8e13380aa5cb777db25 100644 (file)
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -815,7 +815,9 @@ var work struct {
        // mode is the concurrency mode of the current GC cycle.
        mode gcMode
 
-       // Copy of mheap.allspans for marker or sweeper.
+       // Snapshot of mheap.allspans for marker or sweeper created by
+       // gcCopySpans. Unlike allspans, this does not change except
+       // at controlled GC transition points.
        spans []*mspan
 
        // totaltime is the CPU nanoseconds spent in GC since the