Re: [RFC] trace when adding memory to an offline nod

[Michal Hocko <mhocko@suse.com>]

On Wed 23-05-18 10:01:08, Oscar Salvador wrote:
> Hi guys,
> 
> while testing memhotplug, I spotted the following trace:
> 
> =====
> linux kernel: WARNING: CPU: 0 PID: 64 at ./include/linux/gfp.h:467 vmemmap_alloc_block+0x4e/0xc9

This warning is too loud and not really helpful. We are doing
		gfp_t gfp_mask = GFP_KERNEL|__GFP_RETRY_MAYFAIL|__GFP_NOWARN;

		page = alloc_pages_node(node, gfp_mask, order);

so we do not really insist on the allocation succeeding on the requested
node (it is more a hint which node is the best one but we can fallback
to any other node). Moreover we do explicitly do not care about
allocation warnings by __GFP_NOWARN. So maybe we want to soften the
warning like this?

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 036846fc00a6..7f860ea29ec6 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -464,7 +464,7 @@ static inline struct page *
 __alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order)
 {
 	VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
-	VM_WARN_ON(!node_online(nid));
+	VM_WARN_ON((gfp_mask & __GFP_THISNODE) && !node_online(nid));
 
 	return __alloc_pages(gfp_mask, order, nid);
 }
-- 
Michal Hocko
SUSE Labs