Re: [RFC][PATCH 0/2] Quicklist is slighly problematic.

[Robin Holt]

> OK, that's a fatal bug and it's present in 2.6.25.x and 2.6.26.x.  A
> serious issue.
> 
> The patches do apply to both stable kernels and I have tagged them for
> backporting into them.  They're nice and small, but I didn't get a
> really solid yes-this-is-what-we-should-do from Christoph?
> 
> 
> This (from [patch 2/2]): "(Although its patch applied, quicklist can
> waste 64GB on 1TB server (= 1TB / 16), it is still too much??)" is a
> bit of a worry.  Yes, 64GB is too much!  But at least this is now only
> a performance issue rather than a stability issue, yes?

That 64GB is not quite correct.  That assumes all 1TB is free.  The
quicklists are trimmed down as the nodes undergo allocations.  The
problem I see right now is that page tables allocated on one node and
freed on a cpu on a different node could be placed early enough on the
quicklist that it will not be freed until the other node gets under
memory pressure.

Could you give the following a try?  It hasn't even been compiled.  I
think this in addition to your cpus per node change are the right thing
to do.

Thanks,
Robin

Index: ia64-cleanups/include/linux/quicklist.h
===================================================================
--- ia64-cleanups.orig/include/linux/quicklist.h	2008-08-20 21:35:10.000000000 -0500
+++ ia64-cleanups/include/linux/quicklist.h	2008-08-20 21:38:00.891943270 -0500
@@ -66,6 +66,15 @@ static inline void __quicklist_free(int 
 
 static inline void quicklist_free(int nr, void (*dtor)(void *), void *pp)
 {
+#ifdef CONFIG_NUMA
+	unsigned long nid = page_to_nid(virt_to_page(pp));
+
+	if (unlikely(nid != numa_node_id())) {
+		free_page((unsigned long)pp);
+		return;
+	}
+#endif
+
 	__quicklist_free(nr, dtor, pp, virt_to_page(pp));
 }
 
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