linux-kernel - [PATCH v2] mm, slub: print CPU id (and its node) on slab OOM

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Message-ID: <20240814215037.1870645-1-axelrasmussen@google.com>
Date: Wed, 14 Aug 2024 14:50:37 -0700
From: Axel Rasmussen <axelrasmussen@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, 
	David Rientjes <rientjes@...gle.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Pekka Enberg <penberg@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH v2] mm, slub: print CPU id (and its node) on slab OOM

Depending on how remote_node_defrag_ratio is configured, allocations can
end up in this path as a result of the local node being OOM, despite the
allocation overall being unconstrained (node == -1).

When we print a warning, printing the current CPU makes that situation
more clear (i.e., you can immediately see which node's OOM status
matters for the allocation at hand).

Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
---
 mm/slub.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index c9d8a2497fd6..3088260bf75d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3416,14 +3416,15 @@ slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid)
 {
 	static DEFINE_RATELIMIT_STATE(slub_oom_rs, DEFAULT_RATELIMIT_INTERVAL,
 				      DEFAULT_RATELIMIT_BURST);
+	int cpu = raw_smp_processor_id();
 	int node;
 	struct kmem_cache_node *n;
 
 	if ((gfpflags & __GFP_NOWARN) || !__ratelimit(&slub_oom_rs))
 		return;
 
-	pr_warn("SLUB: Unable to allocate memory on node %d, gfp=%#x(%pGg)\n",
-		nid, gfpflags, &gfpflags);
+	pr_warn("SLUB: Unable to allocate memory on CPU %u (of node %d) on node %d, gfp=%#x(%pGg)\n",
+		cpu, cpu_to_node(cpu), nid, gfpflags, &gfpflags);
 	pr_warn("  cache: %s, object size: %u, buffer size: %u, default order: %u, min order: %u\n",
 		s->name, s->object_size, s->size, oo_order(s->oo),
 		oo_order(s->min));
-- 
2.46.0.184.g6999bdac58-goog