[patch -mm 4/9 v2] oom: remove compulsory panic_on_oom mode

[David Rientjes <rientjes@google.com>]

If /proc/sys/vm/panic_on_oom is set to 2, the kernel will panic
regardless of whether the memory allocation is constrained by either a
mempolicy or cpuset.

Since mempolicy-constrained out of memory conditions now iterate through
the tasklist and select a task to kill, it is possible to panic the
machine if all tasks sharing the same mempolicy nodes (including those
with default policy, they may allocate anywhere) or cpuset mems have
/proc/pid/oom_adj values of OOM_DISABLE.  This is functionally equivalent
to the compulsory panic_on_oom setting of 2, so the mode is removed.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 Documentation/sysctl/vm.txt |   20 ++++----------------
 mm/oom_kill.c               |    5 -----
 2 files changed, 4 insertions(+), 21 deletions(-)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -559,25 +559,13 @@ swap-intensive.
 
 panic_on_oom
 
-This enables or disables panic on out-of-memory feature.
+If this is set to zero, the oom killer will be invoked when the kernel is out of
+memory and direct reclaim cannot free any pages.  It will select a memory-
+hogging task that frees up a large amount of memory to kill.
 
-If this is set to 0, the kernel will kill some rogue process,
-called oom_killer.  Usually, oom_killer can kill rogue processes and
-system will survive.
-
-If this is set to 1, the kernel panics when out-of-memory happens.
-However, if a process limits using nodes by mempolicy/cpusets,
-and those nodes become memory exhaustion status, one process
-may be killed by oom-killer. No panic occurs in this case.
-Because other nodes' memory may be free. This means system total status
-may be not fatal yet.
-
-If this is set to 2, the kernel panics compulsorily even on the
-above-mentioned.
+If this is set to non-zero, the machine will panic when out of memory.
 
 The default value is 0.
-1 and 2 are for failover of clustering. Please select either
-according to your policy of failover.
 
 =============================================================
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -672,11 +672,6 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 		/* Got some memory back in the last second. */
 		return;
 
-	if (sysctl_panic_on_oom == 2) {
-		dump_header(NULL, gfp_mask, order, NULL);
-		panic("out of memory. Compulsory panic_on_oom is selected.\n");
-	}
-
 	/*
 	 * Check if there were limitations on the allocation (only relevant for
 	 * NUMA) that may require different handling.

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