Add vm.panic_on_oom sysctl, which enables those who would rather panic than

kill a process, when the system runs out of memory.  Defaults to off.

Usually, this is most useful when the OOM condition is due to mismanagement
of memory, on a system where the applications in question don't respond well
to being killed.

In theory, if the system is properly managed, it shouldn't be possible to
hit this condition. If it does, the panic can be more desirable for some
users (since it can be a good means of finding the root cause) rather than
killing the largest process and continuing on its merry way.

As kib@ mentions in the differential, there is also protect(1), which uses
procctl(PROC_SPROTECT) to ensure that some processes are immune.  However,
a panic approach is still useful in some environments.  This is primarily
intended as a development/debugging tool.

Differential Revision:	D1627
Reviewed by:		kib
MFC after:		1 week

1 files changed, 8 insertions, 0 deletions

diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index c81290ca097d..ecc3dabfe70f 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -180,6 +180,12 @@ static int vm_swap_enabled = 1;
 static int vm_swap_idle_enabled = 0;
 #endif
 
+static int vm_panic_on_oom = 0;
+
+SYSCTL_INT(_vm, OID_AUTO, panic_on_oom,
+	CTLFLAG_RWTUN, &vm_panic_on_oom, 0,
+	"panic on out of memory instead of killing the largest process");
+
 SYSCTL_INT(_vm, OID_AUTO, pageout_wakeup_thresh,
 	CTLFLAG_RW, &vm_pageout_wakeup_thresh, 0,
 	"free page threshold for waking up the pageout daemon");
@@ -1585,6 +1591,8 @@ vm_pageout_oom(int shortage)
 	}
 	sx_sunlock(&allproc_lock);
 	if (bigproc != NULL) {
+		if (vm_panic_on_oom != 0)
+			panic("out of swap space");
 		PROC_LOCK(bigproc);
 		killproc(bigproc, "out of swap space");
 		sched_nice(bigproc, PRIO_MIN);