[PATCH 2/3] slqb: Record what node is local to a kmem_cache_cpu

[Mel Gorman]

When freeing a page, SLQB checks if the page belongs to the local node.
If it is not, it is considered a remote free. On the allocation side, it
always checks the local lists and if they are empty, the page allocator
is called. On memoryless configurations, this is effectively a memory
leak and the machine quickly kills itself in an OOM storm.

This patch records what node ID is closest to a CPU and considers that to be
the local node. As the management structure for the CPU is always allocated
from the closest node, the node the CPU structure resides on is considered
"local".

Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
---
 include/linux/slqb_def.h |    3 +++
 mm/slqb.c                |   23 +++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/linux/slqb_def.h b/include/linux/slqb_def.h
index 1243dda..2ccbe7e 100644
--- a/include/linux/slqb_def.h
+++ b/include/linux/slqb_def.h
@@ -101,6 +101,9 @@ struct kmem_cache_cpu {
 	struct kmem_cache_list	list;		/* List for node-local slabs */
 	unsigned int		colour_next;	/* Next colour offset to use */
 
+	/* local_nid will be numa_node_id() except when memoryless */
+	unsigned int		local_nid;
+
 #ifdef CONFIG_SMP
 	/*
 	 * rlist is a list of objects that don't fit on list.freelist (ie.
diff --git a/mm/slqb.c b/mm/slqb.c
index 4ca85e2..1846480 100644
--- a/mm/slqb.c
+++ b/mm/slqb.c
@@ -1375,7 +1375,7 @@ static noinline void *__slab_alloc_page(struct kmem_cache *s,
 	if (unlikely(!page))
 		return page;
 
-	if (!NUMA_BUILD || likely(slqb_page_to_nid(page) == numa_node_id())) {
+	if (!NUMA_BUILD || likely(slqb_page_to_nid(page) == c->local_nid)) {
 		struct kmem_cache_cpu *c;
 		int cpu = smp_processor_id();
 
@@ -1501,15 +1501,16 @@ static __always_inline void *__slab_alloc(struct kmem_cache *s,
 	struct kmem_cache_cpu *c;
 	struct kmem_cache_list *l;
 
+	c = get_cpu_slab(s, smp_processor_id());
+	VM_BUG_ON(!c);
+
 #ifdef CONFIG_NUMA
-	if (unlikely(node != -1) && unlikely(node != numa_node_id())) {
+	if (unlikely(node != -1) && unlikely(node != c->local_nid)) {
 try_remote:
 		return __remote_slab_alloc(s, gfpflags, node);
 	}
 #endif
 
-	c = get_cpu_slab(s, smp_processor_id());
-	VM_BUG_ON(!c);
 	l = &c->list;
 	object = __cache_list_get_object(s, l);
 	if (unlikely(!object)) {
@@ -1518,7 +1519,7 @@ try_remote:
 			object = __slab_alloc_page(s, gfpflags, node);
 #ifdef CONFIG_NUMA
 			if (unlikely(!object)) {
-				node = numa_node_id();
+				node = c->local_nid;
 				goto try_remote;
 			}
 #endif
@@ -1733,7 +1734,7 @@ static __always_inline void __slab_free(struct kmem_cache *s,
 	slqb_stat_inc(l, FREE);
 
 	if (!NUMA_BUILD || !slab_numa(s) ||
-			likely(slqb_page_to_nid(page) == numa_node_id())) {
+			likely(slqb_page_to_nid(page) == c->local_nid)) {
 		/*
 		 * Freeing fastpath. Collects all local-node objects, not
 		 * just those allocated from our per-CPU list. This allows
@@ -1928,6 +1929,16 @@ static void init_kmem_cache_cpu(struct kmem_cache *s,
 	c->rlist.tail		= NULL;
 	c->remote_cache_list	= NULL;
 #endif
+
+	/*
+	 * Determine what the local node to this CPU is. Ordinarily
+	 * this would be cpu_to_node() but for memoryless nodes, that
+	 * is not the best value. Instead, we take the numa node that
+	 * kmem_cache_cpu is allocated from as being the best guess
+	 * as being local because it'll match what the page allocator
+	 * thinks is the most local
+	 */
+	c->local_nid = page_to_nid(virt_to_page((unsigned long)c & PAGE_MASK));
 }
 
 #ifdef CONFIG_NUMA
-- 
1.6.3.3

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