Consider large page size systems.

go.mod

@@ -14,4 +14,4 @@ require (
 
 retract v0.4.0 // tagged from the wrong branch
 
-replace github.com/tetratelabs/wazero => github.com/ncruces/wazero v0.0.0-20240409112346-f2be6da37a3d
+replace github.com/tetratelabs/wazero => github.com/ncruces/wazero v0.0.0-20240409122832-a4dd11a09060

go.sum

@@ -1,7 +1,7 @@
 github.com/ncruces/julianday v1.0.0 h1:fH0OKwa7NWvniGQtxdJRxAgkBMolni2BjDHaWTxqt7M=
 github.com/ncruces/julianday v1.0.0/go.mod h1:Dusn2KvZrrovOMJuOt0TNXL6tB7U2E8kvza5fFc9G7g=
-github.com/ncruces/wazero v0.0.0-20240409112346-f2be6da37a3d h1:t3S5uhR50fDxrCgoMLcVDFo2jpYdKjq5VWbXFUMHv0w=
-github.com/ncruces/wazero v0.0.0-20240409112346-f2be6da37a3d/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
+github.com/ncruces/wazero v0.0.0-20240409122832-a4dd11a09060 h1:dkYSDM1fMCDttJ6sCdlUHP/BiBzG3hJxDnA+k6zUdyY=
+github.com/ncruces/wazero v0.0.0-20240409122832-a4dd11a09060/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
 github.com/psanford/httpreadat v0.1.0 h1:VleW1HS2zO7/4c7c7zNl33fO6oYACSagjJIyMIwZLUE=
 github.com/psanford/httpreadat v0.1.0/go.mod h1:Zg7P+TlBm3bYbyHTKv/EdtSJZn3qwbPwpfZ/I9GKCRE=
 golang.org/x/crypto v0.22.0 h1:g1v0xeRhjcugydODzvb3mEM9SQ0HGp9s/nh3COQ/C30=

go.work.sum

@@ -1,5 +1,5 @@
-github.com/ncruces/wazero v0.0.0-20240409112346-f2be6da37a3d h1:t3S5uhR50fDxrCgoMLcVDFo2jpYdKjq5VWbXFUMHv0w=
-github.com/ncruces/wazero v0.0.0-20240409112346-f2be6da37a3d/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
+github.com/ncruces/wazero v0.0.0-20240409122832-a4dd11a09060 h1:dkYSDM1fMCDttJ6sCdlUHP/BiBzG3hJxDnA+k6zUdyY=
+github.com/ncruces/wazero v0.0.0-20240409122832-a4dd11a09060/go.mod h1:ytl6Zuh20R/eROuyDaGPkp82O9C/DJfXAwJfQ3X6/7Y=
 golang.org/x/mod v0.8.0 h1:LUYupSeNrTNCGzR/hVBk2NHZO4hXcVaW1k4Qx7rjPx8=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.21.0 h1:AQyQV4dYCvJ7vGmJyKki9+PBdyvhkSd8EIx/qb0AYv4=

internal/util/alloc.go

@@ -10,12 +10,17 @@ import (
 )
 
 func mmappedAllocator(min, cap, max uint64) experimental.MemoryBuffer {
+	// Round up to the page size.
+	rnd := uint64(unix.Getpagesize() - 1)
+	max = (max + rnd) &^ rnd
+	cap = (cap + rnd) &^ rnd
+
 	if max > math.MaxInt {
 		// This ensures int(max) overflows to a negative value,
 		// and unix.Mmap returns EINVAL.
 		max = math.MaxUint64
 	}
-	// Reserve the full max bytes of address space, to ensure we don't need to move it.
+	// Reserve max bytes of address space, to ensure we won't need to move it.
 	// A protected, private, anonymous mapping should not commit memory.
 	b, err := unix.Mmap(-1, 0, int(max), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
 	if err != nil {
@@ -49,18 +54,26 @@ func (m *mmappedBuffer) Buffer() []byte {
 }
 
 func (m *mmappedBuffer) Grow(size uint64) []byte {
-	// Commit additional memory up to size bytes.
-	err := unix.Mprotect(m.buf[len(m.buf):size], unix.PROT_READ|unix.PROT_WRITE)
-	if err != nil {
-		panic(err)
+	if com := uint64(len(m.buf)); com < size {
+		// Round up to the page size.
+		rnd := uint64(unix.Getpagesize() - 1)
+		new := (size + rnd) &^ rnd
+
+		// Commit additional memory up to new bytes.
+		err := unix.Mprotect(m.buf[com:new], unix.PROT_READ|unix.PROT_WRITE)
+		if err != nil {
+			panic(err)
+		}
+
+		// Update commited memory.
+		m.buf = m.buf[:new]
 	}
-	m.buf = m.buf[:size]
 	m.cur = size
 	return m.Buffer()
 }
 
 func (m *mmappedBuffer) Free() {
-	err := unix.Munmap(m.buf)
+	err := unix.Munmap(m.buf[:cap(m.buf)])
 	if err != nil {
 		panic(err)
 	}