runtime: make mheap.pagesInUse an atomic.Uintptr

This change fixes an old TODO that made it a uint64 because it would
make alignment within mheap more complicated. Now that we don't have to
worry about it since we're using atomic types as much as possible,
switch to using a Uintptr. This likely will improve performance a tiny
bit on 32-bit platforms, but really it's mostly cleanup.

Change-Id: Ie705799a111ccad977fc1f43de8b50cf611be303
Reviewed-on: https://go-review.googlesource.com/c/go/+/429221
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Michael Knyszek <[email protected]>

Author: mknyszek

src/runtime/mheap.go

@@ -100,13 +100,11 @@ type mheap struct {
 	// accounting for current progress. If we could only adjust
 	// the slope, it would create a discontinuity in debt if any
 	// progress has already been made.
-	pagesInUse         atomic.Uint64 // pages of spans in stats mSpanInUse
-	pagesSwept         atomic.Uint64 // pages swept this cycle
-	pagesSweptBasis    atomic.Uint64 // pagesSwept to use as the origin of the sweep ratio
-	sweepHeapLiveBasis uint64        // value of gcController.heapLive to use as the origin of sweep ratio; written with lock, read without
-	sweepPagesPerByte  float64       // proportional sweep ratio; written with lock, read without
-	// TODO(austin): pagesInUse should be a uintptr, but the 386
-	// compiler can't 8-byte align fields.
+	pagesInUse         atomic.Uintptr // pages of spans in stats mSpanInUse
+	pagesSwept         atomic.Uint64  // pages swept this cycle
+	pagesSweptBasis    atomic.Uint64  // pagesSwept to use as the origin of the sweep ratio
+	sweepHeapLiveBasis uint64         // value of gcController.heapLive to use as the origin of sweep ratio; written with lock, read without
+	sweepPagesPerByte  float64        // proportional sweep ratio; written with lock, read without
 
 	// Page reclaimer state
 
@@ -1379,7 +1377,7 @@ HaveSpan:
 		atomic.Or8(&arena.pageInUse[pageIdx], pageMask)
 
 		// Update related page sweeper stats.
-		h.pagesInUse.Add(int64(npages))
+		h.pagesInUse.Add(npages)
 	}
 
 	// Make sure the newly allocated span will be observed
@@ -1529,7 +1527,7 @@ func (h *mheap) freeSpanLocked(s *mspan, typ spanAllocType) {
 			print("mheap.freeSpanLocked - span ", s, " ptr ", hex(s.base()), " allocCount ", s.allocCount, " sweepgen ", s.sweepgen, "/", h.sweepgen, "\n")
 			throw("mheap.freeSpanLocked - invalid free")
 		}
-		h.pagesInUse.Add(-int64(s.npages))
+		h.pagesInUse.Add(-s.npages)
 
 		// Clear in-use bit in arena page bitmap.
 		arena, pageIdx, pageMask := pageIndexOf(s.base())