2 files changed, 29 insertions, 0 deletions
diff --git a/cmd/ioworkload/scenario_mmap.go b/cmd/ioworkload/scenario_mmap.go
index e7b9f02..0d953d2 100644
--- a/cmd/ioworkload/scenario_mmap.go
+++ b/cmd/ioworkload/scenario_mmap.go
@@ -7,6 +7,8 @@ import (
 	"unsafe"
 )
 
+const mremapMayMove = 1
+
 // mmapBasic creates a file-backed shared mapping.
 // mmap(2) allows closing the fd after mapping without invalidating the mapping.
 func mmapBasic() error {
@@ -108,3 +110,29 @@ func mmapMsyncInvalidFlags() error {
 	}
 	return nil
 }
+
+// mmapMremapMunmap remaps an anonymous mapping and unmaps the resized region.
+// It is used to validate enter_mremap/enter_munmap tracing and memory-byte
+// accounting separation from I/O bytes.
+func mmapMremapMunmap() error {
+	const pageSize = 4096
+
+	mapped, err := syscall.Mmap(-1, 0, pageSize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
+	if err != nil {
+		return fmt.Errorf("mmap: %w", err)
+	}
+
+	oldAddr := uintptr(unsafe.Pointer(&mapped[0]))
+	newSize := uintptr(pageSize * 2)
+	newAddr, _, errno := syscall.Syscall6(syscall.SYS_MREMAP, oldAddr, uintptr(len(mapped)), newSize, mremapMayMove, 0, 0)
+	if errno != 0 {
+		_ = syscall.Munmap(mapped)
+		return fmt.Errorf("mremap: %w", errno)
+	}
+
+	_, _, errno = syscall.Syscall(syscall.SYS_MUNMAP, newAddr, newSize, 0)
+	if errno != 0 {
+		return fmt.Errorf("munmap: %w", errno)
+	}
+	return nil
+}
diff --git a/cmd/ioworkload/scenarios.go b/cmd/ioworkload/scenarios.go
index 6a6e40b..8f4eef2 100644
--- a/cmd/ioworkload/scenarios.go
+++ b/cmd/ioworkload/scenarios.go
@@ -99,6 +99,7 @@ var scenarios = map[string]func() error{
 	"mmap-basic":                    mmapBasic,
 	"mmap-msync-sync":               mmapMsyncSync,
 	"mmap-msync-invalid-flags":      mmapMsyncInvalidFlags,
+	"mmap-mremap-munmap":            mmapMremapMunmap,
 	"copy-file-range-basic":         copyFileRangeBasic,
 	"copy-file-range-bad-dst-fd":    copyFileRangeBadDstFd,
 	"truncate-basic":                truncateBasic,