runtime: integrate new page allocator into runtime

This change integrates all the bits and pieces of the new page allocator
into the runtime, behind a global constant.

Updates #35112.

Change-Id: I6696bde7bab098a498ab37ed2a2caad2a05d30ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/201764
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/export_test.go

@@ -12,6 +12,8 @@ import (
 	"unsafe"
 )
 
+const OldPageAllocator = oldPageAllocator
+
 var Fadd64 = fadd64
 var Fsub64 = fsub64
 var Fmul64 = fmul64
@@ -354,8 +356,15 @@ func ReadMemStatsSlow() (base, slow MemStats) {
 			slow.BySize[i].Frees = bySize[i].Frees
 		}
 
-		for i := mheap_.free.start(0, 0); i.valid(); i = i.next() {
-			slow.HeapReleased += uint64(i.span().released())
+		if oldPageAllocator {
+			for i := mheap_.free.start(0, 0); i.valid(); i = i.next() {
+				slow.HeapReleased += uint64(i.span().released())
+			}
+		} else {
+			for i := mheap_.pages.start; i < mheap_.pages.end; i++ {
+				pg := mheap_.pages.chunks[i].scavenged.popcntRange(0, pallocChunkPages)
+				slow.HeapReleased += uint64(pg) * pageSize
+			}
 		}
 
 		// Unused space in the current arena also counts as released space.
@@ -974,3 +983,49 @@ var BaseChunkIdx = ChunkIdx(chunkIndex((0xc000*pageAlloc64Bit + 0x200*pageAlloc3
 func PageBase(c ChunkIdx, pageIdx uint) uintptr {
 	return chunkBase(chunkIdx(c)) + uintptr(pageIdx)*pageSize
 }
+
+type BitsMismatch struct {
+	Base      uintptr
+	Got, Want uint64
+}
+
+func CheckScavengedBitsCleared(mismatches []BitsMismatch) (n int, ok bool) {
+	ok = true
+
+	// Run on the system stack to avoid stack growth allocation.
+	systemstack(func() {
+		getg().m.mallocing++
+
+		// Lock so that we can safely access the bitmap.
+		lock(&mheap_.lock)
+	chunkLoop:
+		for i := mheap_.pages.start; i < mheap_.pages.end; i++ {
+			chunk := &mheap_.pages.chunks[i]
+			for j := 0; j < pallocChunkPages/64; j++ {
+				// Run over each 64-bit bitmap section and ensure
+				// scavenged is being cleared properly on allocation.
+				// If a used bit and scavenged bit are both set, that's
+				// an error, and could indicate a larger problem, or
+				// an accounting problem.
+				want := chunk.scavenged[j] &^ chunk.pallocBits[j]
+				got := chunk.scavenged[j]
+				if want != got {
+					ok = false
+					if n >= len(mismatches) {
+						break chunkLoop
+					}
+					mismatches[n] = BitsMismatch{
+						Base: chunkBase(i) + uintptr(j)*64*pageSize,
+						Got:  got,
+						Want: want,
+					}
+					n++
+				}
+			}
+		}
+		unlock(&mheap_.lock)
+
+		getg().m.mallocing--
+	})
+	return
+}

src/runtime/gc_test.go

@@ -465,6 +465,10 @@ func TestReadMemStats(t *testing.T) {
 }
 
 func TestUnscavHugePages(t *testing.T) {
+	if !runtime.OldPageAllocator {
+		// This test is only relevant for the old page allocator.
+		return
+	}
 	// Allocate 20 MiB and immediately free it a few times to increase
 	// the chance that unscavHugePages isn't zero and that some kind of
 	// accounting had to happen in the runtime.

src/runtime/malloc.go

@@ -322,6 +322,9 @@ const (
 	//
 	// This should agree with minZeroPage in the compiler.
 	minLegalPointer uintptr = 4096
+
+	// Whether to use the old page allocator or not.
+	oldPageAllocator = true
 )
 
 // physPageSize is the size in bytes of the OS's physical pages.

src/runtime/malloc_test.go

@@ -176,6 +176,23 @@ func TestPhysicalMemoryUtilization(t *testing.T) {
 	}
 }
 
+func TestScavengedBitsCleared(t *testing.T) {
+	if OldPageAllocator {
+		// This test is only relevant for the new page allocator.
+		return
+	}
+	var mismatches [128]BitsMismatch
+	if n, ok := CheckScavengedBitsCleared(mismatches[:]); !ok {
+		t.Errorf("uncleared scavenged bits")
+		for _, m := range mismatches[:n] {
+			t.Logf("\t@ address 0x%x", m.Base)
+			t.Logf("\t|  got: %064b", m.Got)
+			t.Logf("\t| want: %064b", m.Want)
+		}
+		t.FailNow()
+	}
+}
+
 type acLink struct {
 	x [1 << 20]byte
 }

src/runtime/mgcscavenge.go

@@ -136,6 +136,9 @@ func gcPaceScavenger() {
 		return
 	}
 	mheap_.scavengeGoal = retainedGoal
+	if !oldPageAllocator {
+		mheap_.pages.resetScavengeAddr()
+	}
 }
 
 // Sleep/wait state of the background scavenger.
@@ -250,12 +253,21 @@ func bgscavenge(c chan int) {
 				return
 			}
 
-			// Scavenge one page, and measure the amount of time spent scavenging.
-			start := nanotime()
-			released = mheap_.scavengeLocked(physPageSize)
-			crit = nanotime() - start
+			if oldPageAllocator {
+				// Scavenge one page, and measure the amount of time spent scavenging.
+				start := nanotime()
+				released = mheap_.scavengeLocked(physPageSize)
+				crit = nanotime() - start
 
-			unlock(&mheap_.lock)
+				unlock(&mheap_.lock)
+			} else {
+				unlock(&mheap_.lock)
+
+				// Scavenge one page, and measure the amount of time spent scavenging.
+				start := nanotime()
+				released = mheap_.pages.scavengeOne(physPageSize, false)
+				crit = nanotime() - start
+			}
 		})
 
 		if debug.gctrace > 0 {

src/runtime/mheap.go

@@ -32,10 +32,11 @@ type mheap struct {
 	// lock must only be acquired on the system stack, otherwise a g
 	// could self-deadlock if its stack grows with the lock held.
 	lock      mutex
-	free      mTreap // free spans
-	sweepgen  uint32 // sweep generation, see comment in mspan
-	sweepdone uint32 // all spans are swept
-	sweepers  uint32 // number of active sweepone calls
+	free      mTreap    // free spans
+	pages     pageAlloc // page allocation data structure
+	sweepgen  uint32    // sweep generation, see comment in mspan
+	sweepdone uint32    // all spans are swept
+	sweepers  uint32    // number of active sweepone calls
 
 	// allspans is a slice of all mspans ever created. Each mspan
 	// appears exactly once.
@@ -852,6 +853,10 @@ func (h *mheap) init() {
 	for i := range h.central {
 		h.central[i].mcentral.init(spanClass(i))
 	}
+
+	if !oldPageAllocator {
+		h.pages.init(&h.lock, &memstats.gc_sys)
+	}
 }
 
 // reclaim sweeps and reclaims at least npage pages into the heap.
@@ -1208,6 +1213,47 @@ func (h *mheap) setSpans(base, npage uintptr, s *mspan) {
 // The returned span has been removed from the
 // free structures, but its state is still mSpanFree.
 func (h *mheap) allocSpanLocked(npage uintptr, stat *uint64) *mspan {
+	if oldPageAllocator {
+		return h.allocSpanLockedOld(npage, stat)
+	}
+	base, scav := h.pages.alloc(npage)
+	if base != 0 {
+		goto HaveBase
+	}
+	if !h.grow(npage) {
+		return nil
+	}
+	base, scav = h.pages.alloc(npage)
+	if base != 0 {
+		goto HaveBase
+	}
+	throw("grew heap, but no adequate free space found")
+
+HaveBase:
+	if scav != 0 {
+		// sysUsed all the pages that are actually available
+		// in the span.
+		sysUsed(unsafe.Pointer(base), npage*pageSize)
+		memstats.heap_released -= uint64(scav)
+	}
+
+	s := (*mspan)(h.spanalloc.alloc())
+	s.init(base, npage)
+	// TODO(mknyszek): Add code to compute whether the newly-allocated
+	// region needs to be zeroed.
+	s.needzero = 1
+	h.setSpans(s.base(), npage, s)
+
+	*stat += uint64(npage << _PageShift)
+	memstats.heap_idle -= uint64(npage << _PageShift)
+
+	return s
+}
+
+// Allocates a span of the given size.  h must be locked.
+// The returned span has been removed from the
+// free structures, but its state is still mSpanFree.
+func (h *mheap) allocSpanLockedOld(npage uintptr, stat *uint64) *mspan {
 	t := h.free.find(npage)
 	if t.valid() {
 		goto HaveSpan
@@ -1291,7 +1337,12 @@ HaveSpan:
 // h must be locked.
 func (h *mheap) grow(npage uintptr) bool {
 	ask := npage << _PageShift
+	if !oldPageAllocator {
+		// We must grow the heap in whole palloc chunks.
+		ask = alignUp(ask, pallocChunkBytes)
+	}
 
+	totalGrowth := uintptr(0)
 	nBase := alignUp(h.curArena.base+ask, physPageSize)
 	if nBase > h.curArena.end {
 		// Not enough room in the current arena. Allocate more
@@ -1312,7 +1363,12 @@ func (h *mheap) grow(npage uintptr) bool {
 			// remains of the current space and switch to
 			// the new space. This should be rare.
 			if size := h.curArena.end - h.curArena.base; size != 0 {
-				h.growAddSpan(unsafe.Pointer(h.curArena.base), size)
+				if oldPageAllocator {
+					h.growAddSpan(unsafe.Pointer(h.curArena.base), size)
+				} else {
+					h.pages.grow(h.curArena.base, size)
+				}
+				totalGrowth += size
 			}
 			// Switch to the new space.
 			h.curArena.base = uintptr(av)
@@ -1338,7 +1394,24 @@ func (h *mheap) grow(npage uintptr) bool {
 	// Grow into the current arena.
 	v := h.curArena.base
 	h.curArena.base = nBase
-	h.growAddSpan(unsafe.Pointer(v), nBase-v)
+	if oldPageAllocator {
+		h.growAddSpan(unsafe.Pointer(v), nBase-v)
+	} else {
+		h.pages.grow(v, nBase-v)
+		totalGrowth += nBase - v
+
+		// We just caused a heap growth, so scavenge down what will soon be used.
+		// By scavenging inline we deal with the failure to allocate out of
+		// memory fragments by scavenging the memory fragments that are least
+		// likely to be re-used.
+		if retained := heapRetained(); retained+uint64(totalGrowth) > h.scavengeGoal {
+			todo := totalGrowth
+			if overage := uintptr(retained + uint64(totalGrowth) - h.scavengeGoal); todo > overage {
+				todo = overage
+			}
+			h.pages.scavenge(todo, true)
+		}
+	}
 	return true
 }
 
@@ -1442,13 +1515,24 @@ func (h *mheap) freeSpanLocked(s *mspan, acctinuse, acctidle bool) {
 	if acctidle {
 		memstats.heap_idle += uint64(s.npages << _PageShift)
 	}
-	s.state.set(mSpanFree)
 
-	// Coalesce span with neighbors.
-	h.coalesce(s)
+	if oldPageAllocator {
+		s.state.set(mSpanFree)
 
-	// Insert s into the treap.
-	h.free.insert(s)
+		// Coalesce span with neighbors.
+		h.coalesce(s)
+
+		// Insert s into the treap.
+		h.free.insert(s)
+		return
+	}
+
+	// Mark the space as free.
+	h.pages.free(s.base(), s.npages)
+
+	// Free the span structure. We no longer have a use for it.
+	s.state.set(mSpanDead)
+	h.spanalloc.free(unsafe.Pointer(s))
 }
 
 // scavengeSplit takes t.span() and attempts to split off a span containing size
@@ -1573,7 +1657,12 @@ func (h *mheap) scavengeAll() {
 	gp := getg()
 	gp.m.mallocing++
 	lock(&h.lock)
-	released := h.scavengeLocked(^uintptr(0))
+	var released uintptr
+	if oldPageAllocator {
+		released = h.scavengeLocked(^uintptr(0))
+	} else {
+		released = h.pages.scavenge(^uintptr(0), true)
+	}
 	unlock(&h.lock)
 	gp.m.mallocing--