Add AvailableMemory for Linux

Author: dustin-decker

doc.go

@@ -22,3 +22,13 @@ func TotalMemory() uint64 {
 func FreeMemory() uint64 {
 	return sysFreeMemory()
 }
+
+// AvailableMemory returns the total free+freeable system memory in bytes.
+//
+// The total available memory is the free memory + freeable memory
+// such as buffer and cache.
+//
+// If free memory size could not be determined, then 0 is returned.
+func AvailableMemory() uint64 {
+	return sysAvailableMemory()
+}

memory_bsd.go

@@ -1,3 +1,4 @@
+//go:build freebsd || openbsd || dragonfly || netbsd
 // +build freebsd openbsd dragonfly netbsd
 
 package memory
@@ -17,3 +18,7 @@ func sysFreeMemory() uint64 {
 	}
 	return s
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}

memory_darwin.go

@@ -1,3 +1,4 @@
+//go:build darwin
 // +build darwin
 
 package memory
@@ -47,3 +48,7 @@ func sysFreeMemory() uint64 {
 	}
 	return freePages * pageSize
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}

memory_linux.go

@@ -1,3 +1,4 @@
+//go:build linux
 // +build linux
 
 package memory
@@ -27,3 +28,18 @@ func sysFreeMemory() uint64 {
 	// So we always convert to uint64 to match signature.
 	return uint64(in.Freeram) * uint64(in.Unit)
 }
+
+func sysAvailableMemory() uint64 {
+	in := &syscall.Sysinfo_t{}
+	err := syscall.Sysinfo(in)
+	if err != nil {
+		return 0
+	}
+	// If this is a 32-bit system, then these fields are
+	// uint32 instead of uint64.
+	// So we always convert to uint64 to match signature.
+	// Buffer/cache ram is included on linux since the kernel
+	// will free this memory for applications if needed, and tends
+	// to use almost all free memory for itself when it can.
+	return (uint64(in.Freeram) + uint64(in.Bufferram)) * uint64(in.Unit)
+}

memory_windows.go

@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package memory
@@ -58,3 +59,7 @@ func sysFreeMemory() uint64 {
 	}
 	return msx.ullAvailPhys
 }
+
+func sysAvailableMemory() uint64 {
+	return sysFreeMemory()
+}