[patch 10/10 -mm v3] oom: default to killing current for pagefault ooms

[David Rientjes <rientjes@google.com>]

The pagefault oom handler does not know the context (gfp_mask, order,
etc) in which memory was not found when a VM_FAULT_OOM is generated.  The
only information known is that current is trying to allocate in that
context, so killing it is a legitimate response (and is the default for
architectures that do not even use the pagefault oom handler such as ia64
and powerpc).

When a VM_FAULT_OOM occurs, the pagefault oom handler will now attempt to
kill current by default.  If it is unkillable, the oom killer is called
to find a memory-hogging task to kill instead that will lead to future
memory freeing.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   18 +++++++++++++-----
 1 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -711,15 +711,23 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 }
 
 /*
- * The pagefault handler calls here because it is out of memory, so kill a
- * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel
- * oom killing is already in progress so do nothing.  If a task is found with
- * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
+ * The pagefault handler calls here because it is out of memory, so kill current
+ * by default.  If it's unkillable, then fallback to killing a memory-hogging
+ * task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel oom killing is
+ * already in progress so do nothing.  If a task is found with TIF_MEMDIE set,
+ * it has been killed so do nothing and allow it to exit.
  */
 void pagefault_out_of_memory(void)
 {
+	unsigned long totalpages;
+	int err;
+
 	if (try_set_system_oom()) {
-		out_of_memory(NULL, 0, 0, NULL);
+		constrained_alloc(NULL, 0, NULL, &totalpages);
+		err = oom_kill_process(current, 0, 0, 0, totalpages, NULL,
+					"Out of memory (pagefault)");
+		if (err)
+			out_of_memory(NULL, 0, 0, NULL);
 		clear_system_oom();
 	}
 	if (!test_thread_flag(TIF_MEMDIE))

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