Index: pym/portage/__init__.py
===================================================================
--- pym/portage/__init__.py	(revision 11181)
+++ pym/portage/__init__.py	(revision 11182)
@@ -996,7 +996,8 @@
 		"PORTAGE_ELOG_MAILURI", "PORTAGE_ELOG_SYSTEM",
 		"PORTAGE_FETCH_CHECKSUM_TRY_MIRRORS", "PORTAGE_FETCH_RESUME_MIN_SIZE",
 		"PORTAGE_GPG_DIR",
-		"PORTAGE_GPG_KEY", "PORTAGE_PACKAGE_EMPTY_ABORT",
+		"PORTAGE_GPG_KEY", "PORTAGE_IONICE_COMMAND",
+		"PORTAGE_PACKAGE_EMPTY_ABORT",
 		"PORTAGE_RO_DISTDIRS",
 		"PORTAGE_RSYNC_EXTRA_OPTS", "PORTAGE_RSYNC_OPTS",
 		"PORTAGE_RSYNC_RETRIES", "PORTAGE_USE", "PORT_LOGDIR",
Index: pym/_emerge/__init__.py
===================================================================
--- pym/_emerge/__init__.py	(revision 11181)
+++ pym/_emerge/__init__.py	(revision 11182)
@@ -12846,6 +12846,29 @@
 		settings["NOCOLOR"] = "true"
 		settings.backup_changes("NOCOLOR")
 
+def ionice(settings):
+
+	ionice_cmd = settings.get("PORTAGE_IONICE_COMMAND")
+	if ionice_cmd:
+		ionice_cmd = shlex.split(ionice_cmd)
+	if not ionice_cmd:
+		return
+
+	from portage.util import varexpand
+	variables = {"PID" : str(os.getpid())}
+	cmd = [varexpand(x, mydict=variables) for x in ionice_cmd]
+
+	try:
+		rval = portage.process.spawn(cmd, env=os.environ)
+	except portage.exception.CommandNotFound:
+		# The OS kernel probably doesn't support ionice,
+		# so return silently.
+		return
+
+	if rval != os.EX_OK:
+		out = portage.output.EOutput()
+		out.eerror("PORTAGE_IONICE_COMMAND returned %d" % (rval,))
+
 def emerge_main():
 	global portage	# NFC why this is necessary now - genone
 	portage._disable_legacy_globals()
@@ -12867,6 +12890,8 @@
 	settings, trees, mtimedb = load_emerge_config()
 	portdb = trees[settings["ROOT"]]["porttree"].dbapi
 
+	ionice(settings)
+
 	try:
 		os.nice(int(settings.get("PORTAGE_NICENESS", "0")))
 	except (OSError, ValueError), e:
Index: cnf/make.globals
===================================================================
--- cnf/make.globals	(revision 11181)
+++ cnf/make.globals	(revision 11182)
@@ -62,6 +62,9 @@
 # Minimum size of existing file for RESUMECOMMAND to be called.
 PORTAGE_FETCH_RESUME_MIN_SIZE="350K"
 
+# Command called to adjust the io priority of portage and it's subprocesses.
+PORTAGE_IONICE_COMMAND="ionice -c 2 -n 7 -p \${PID}"
+
 # Number of times 'emerge --sync' will run before giving up.
 PORTAGE_RSYNC_RETRIES="3"
 
Index: man/make.conf.5
===================================================================
--- man/make.conf.5	(revision 11181)
+++ man/make.conf.5	(revision 11182)
@@ -459,6 +459,14 @@
 variable should contain an integer number of bytes and may have a suffix such
 as K, M, or G.
 .TP
+\fBPORTAGE_IONICE_COMMAND\fR = \fI[ionice command string]\fR
+This variable should contain a command for portage to call in order
+to adjust the io priority of portage and it's subprocesses. The command
+string should contain a \\${PID} place-holder that will be substituted
+with an integer pid. For more information about ionice, see \fBionice\fR(1).
+.br
+Defaults to "ionice -c 2 -n 7 -p \\${PID}".
+.TP
 \fBPORTAGE_NICENESS\fR = \fI[number]\fR
 The value of this variable will be added to the current nice level that
 emerge is running at.  In other words, this will not set the nice level,