[PATCH 04 of 16] serialize oom killer

[Andrea Arcangeli <andrea@suse.de>]

# HG changeset patch
# User Andrea Arcangeli <andrea@suse.de>
# Date 1181332960 -7200
# Node ID baa866fedc79cb333b90004da2730715c145f1d5
# Parent  532a5f712848ee75d827bfe233b9364a709e1fc1
serialize oom killer

It's risky and useless to run two oom killers in parallel, let serialize it to
reduce the probability of spurious oom-killage.

Signed-off-by: Andrea Arcangeli <andrea@suse.de>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -400,12 +400,15 @@ void out_of_memory(struct zonelist *zone
 	unsigned long points = 0;
 	unsigned long freed = 0;
 	int constraint;
+	static DECLARE_MUTEX(OOM_lock);
 
 	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 	if (freed > 0)
 		/* Got some memory back in the last second. */
 		return;
 
+	if (down_trylock(&OOM_lock))
+		return;
 	if (printk_ratelimit()) {
 		printk(KERN_WARNING "%s invoked oom-killer: "
 			"gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
@@ -472,4 +475,6 @@ out:
 	 */
 	if (!test_thread_flag(TIF_MEMDIE))
 		schedule_timeout_uninterruptible(1);
-}
+
+	up(&OOM_lock);
+}

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