[PATCH] oom-killer trigger

[Rik van Riel <riel@conectiva.com.br>]

Hi,

the OOM killer in Linux 2.4 has a rather embarrasing bug.

1. the OOM killer never triggers if we have > freepages.min
   of free memory
2. __alloc_pages() never allocates pages to < freepages.min
   for user allocations

==> the OOM killer never gets triggered under some workloads;
    the system just sits around with nr_free_pages == freepages.min

The patch below trivially fixes this by upping the OOM kill limit
by a really small number of pages ...

Now lets hope it won't trigger too early (but since it'll only
trigger when we're completely out of swap, etc...).

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

		http://www.surriel.com/
http://www.conectiva.com/	http://distro.conectiva.com/


--- mm/oom_kill.c.orig	Thu Mar  1 18:57:11 2001
+++ mm/oom_kill.c	Thu Mar  1 18:58:23 2001
@@ -188,13 +188,17 @@
  *
  * Returns 0 if there is still enough memory left,
  * 1 when we are out of memory (otherwise).
+ *
+ * Note that since __alloc_pages() never lets user
+ * allocations go below freepages.min, we have to
+ * use a slightly higher threshold here...
  */
 int out_of_memory(void)
 {
 	struct sysinfo swp_info;

 	/* Enough free memory?  Not OOM. */
-	if (nr_free_pages() > freepages.min)
+	if (nr_free_pages() > freepages.min + 4)
 		return 0;

 	if (nr_free_pages() + nr_inactive_clean_pages() > freepages.low)

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