slub: Fallback to minimal order during slab page allocation
If any higher order allocation fails then fall back the smallest order
necessary to contain at least one object. This enables fallback for all
allocations to order 0 pages. The fallback will waste more memory (objects
will not fit neatly) and the fallback slabs will be not as efficient as larger
slabs since they contain less objects.
Note that SLAB also depends on order 1 allocations for some slabs that waste
too much memory if forced into PAGE_SIZE'd page. SLUB now can now deal with
failing order 1 allocs which SLAB cannot do.
Add a new field min that will contain the objects for the smallest possible order
for a slab cache.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
diff --git a/mm/slub.c b/mm/slub.c
index c8514e9..35c22d9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1113,28 +1113,43 @@
/*
* Slab allocation and freeing
*/
+static inline struct page *alloc_slab_page(gfp_t flags, int node,
+ struct kmem_cache_order_objects oo)
+{
+ int order = oo_order(oo);
+
+ if (node == -1)
+ return alloc_pages(flags, order);
+ else
+ return alloc_pages_node(node, flags, order);
+}
+
static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
{
struct page *page;
struct kmem_cache_order_objects oo = s->oo;
- int order = oo_order(oo);
- int pages = 1 << order;
flags |= s->allocflags;
- if (node == -1)
- page = alloc_pages(flags, order);
- else
- page = alloc_pages_node(node, flags, order);
+ page = alloc_slab_page(flags | __GFP_NOWARN | __GFP_NORETRY, node,
+ oo);
+ if (unlikely(!page)) {
+ oo = s->min;
+ /*
+ * Allocation may have failed due to fragmentation.
+ * Try a lower order alloc if possible
+ */
+ page = alloc_slab_page(flags, node, oo);
+ if (!page)
+ return NULL;
- if (!page)
- return NULL;
-
+ stat(get_cpu_slab(s, raw_smp_processor_id()), ORDER_FALLBACK);
+ }
page->objects = oo_objects(oo);
mod_zone_page_state(page_zone(page),
(s->flags & SLAB_RECLAIM_ACCOUNT) ?
NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
- pages);
+ 1 << oo_order(oo));
return page;
}
@@ -2347,6 +2362,7 @@
* Determine the number of objects per slab
*/
s->oo = oo_make(order, size);
+ s->min = oo_make(get_order(size), size);
if (oo_objects(s->oo) > oo_objects(s->max))
s->max = s->oo;
@@ -4163,7 +4179,7 @@
STAT_ATTR(DEACTIVATE_TO_HEAD, deactivate_to_head);
STAT_ATTR(DEACTIVATE_TO_TAIL, deactivate_to_tail);
STAT_ATTR(DEACTIVATE_REMOTE_FREES, deactivate_remote_frees);
-
+STAT_ATTR(ORDER_FALLBACK, order_fallback);
#endif
static struct attribute *slab_attrs[] = {
@@ -4216,6 +4232,7 @@
&deactivate_to_head_attr.attr,
&deactivate_to_tail_attr.attr,
&deactivate_remote_frees_attr.attr,
+ &order_fallback_attr.attr,
#endif
NULL
};