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Subject[PATCH 2/4] slqb: Record what node is local to a kmem_cache_cpu
Date
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 considered local to a CPU. 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@csn.ul.ie>
---
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 4d72be2..89fd8e4 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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