runtime: add new page allocator core

This change adds a new bitmap-based allocator to the runtime with tests.
It does not yet integrate the page allocator into the runtime and thus
this change is almost purely additive.

Updates #35112.

Change-Id: Ic3d024c28abee8be8797d3918116a80f901cc2bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/190622
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/src/runtime/mpagealloc_32bit.go b/src/runtime/mpagealloc_32bit.go
index c91b2bbe3f..996228c046 100644
--- a/src/runtime/mpagealloc_32bit.go
+++ b/src/runtime/mpagealloc_32bit.go
@@ -17,7 +17,93 @@
 
 package runtime
 
+import "unsafe"
+
 const (
 	// The number of levels in the radix tree.
 	summaryLevels = 4
+
+	// Constants for testing.
+	pageAlloc32Bit = 1
+	pageAlloc64Bit = 0
 )
+
+// See comment in mpagealloc_64bit.go.
+var levelBits = [summaryLevels]uint{
+	summaryL0Bits,
+	summaryLevelBits,
+	summaryLevelBits,
+	summaryLevelBits,
+}
+
+// See comment in mpagealloc_64bit.go.
+var levelShift = [summaryLevels]uint{
+	heapAddrBits - summaryL0Bits,
+	heapAddrBits - summaryL0Bits - 1*summaryLevelBits,
+	heapAddrBits - summaryL0Bits - 2*summaryLevelBits,
+	heapAddrBits - summaryL0Bits - 3*summaryLevelBits,
+}
+
+// See comment in mpagealloc_64bit.go.
+var levelLogPages = [summaryLevels]uint{
+	logPallocChunkPages + 3*summaryLevelBits,
+	logPallocChunkPages + 2*summaryLevelBits,
+	logPallocChunkPages + 1*summaryLevelBits,
+	logPallocChunkPages,
+}
+
+// See mpagealloc_64bit.go for details.
+func (s *pageAlloc) sysInit() {
+	// Calculate how much memory all our entries will take up.
+	//
+	// This should be around 12 KiB or less.
+	totalSize := uintptr(0)
+	for l := 0; l < summaryLevels; l++ {
+		totalSize += (uintptr(1) << (heapAddrBits - levelShift[l])) * pallocSumBytes
+	}
+	totalSize = alignUp(totalSize, physPageSize)
+
+	// Reserve memory for all levels in one go. There shouldn't be much for 32-bit.
+	reservation := sysReserve(nil, totalSize)
+	if reservation == nil {
+		throw("failed to reserve page summary memory")
+	}
+	// There isn't much. Just map it and mark it as used immediately.
+	sysMap(reservation, totalSize, s.sysStat)
+	sysUsed(reservation, totalSize)
+
+	// Iterate over the reservation and cut it up into slices.
+	//
+	// Maintain i as the byte offset from reservation where
+	// the new slice should start.
+	for l, shift := range levelShift {
+		entries := 1 << (heapAddrBits - shift)
+
+		// Put this reservation into a slice.
+		sl := notInHeapSlice{(*notInHeap)(reservation), 0, entries}
+		s.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))
+
+		reservation = add(reservation, uintptr(entries)*pallocSumBytes)
+	}
+}
+
+// See mpagealloc_64bit.go for details.
+func (s *pageAlloc) sysGrow(base, limit uintptr) {
+	if base%pallocChunkBytes != 0 || limit%pallocChunkBytes != 0 {
+		print("runtime: base = ", hex(base), ", limit = ", hex(limit), "\n")
+		throw("sysGrow bounds not aligned to pallocChunkBytes")
+	}
+
+	// Walk up the tree and update the summary slices.
+	for l := len(s.summary) - 1; l >= 0; l-- {
+		// Figure out what part of the summary array this new address space needs.
+		// Note that we need to align the ranges to the block width (1<<levelBits[l])
+		// at this level because the full block is needed to compute the summary for
+		// the next level.
+		lo, hi := addrsToSummaryRange(l, base, limit)
+		_, hi = blockAlignSummaryRange(l, lo, hi)
+		if hi > len(s.summary[l]) {
+			s.summary[l] = s.summary[l][:hi]
+		}
+	}
+}