On Mon, Jan 26, 2015 at 01:53:32PM -0600, Christoph Lameter wrote:
> On Mon, 26 Jan 2015, Vladimir Davydov wrote:
>
> > We could do that, but IMO that would only complicate the code w/o
> > yielding any real benefits. This function is slow and called rarely
> > anyway, so I don't think there is any point to optimize out a page
> > allocation here.
>
> I think you already have the code there. Simply allow the sizeing of the
> empty_page[] array. And rename it.
>
May be, we could remove this allocation at all then? I mean, always
distribute slabs among constant number of buckets, say 32, like this:
diff --git a/mm/slub.c b/mm/slub.c
index 5ed1a73e2ec8..a43b213770b4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3358,6 +3358,8 @@ void kfree(const void *x)
}
EXPORT_SYMBOL(kfree);
+#define SHRINK_BUCKETS 32
+
/*
* kmem_cache_shrink removes empty slabs from the partial lists and sorts
* the remaining slabs by the number of items in use. The slabs with the
@@ -3376,19 +3378,15 @@ int __kmem_cache_shrink(struct kmem_cache *s)
struct page *page;
struct page *t;
int objects = oo_objects(s->max);
- struct list_head *slabs_by_inuse =
- kmalloc(sizeof(struct list_head) * objects, GFP_KERNEL);
+ struct list_head slabs_by_inuse[SHRINK_BUCKETS];
unsigned long flags;
- if (!slabs_by_inuse)
- return -ENOMEM;
-
flush_all(s);
for_each_kmem_cache_node(s, node, n) {
if (!n->nr_partial)
continue;
- for (i = 0; i < objects; i++)
+ for (i = 0; i < SHRINK_BUCKETS; i++)
INIT_LIST_HEAD(slabs_by_inuse + i);
spin_lock_irqsave(&n->list_lock, flags);
@@ -3400,7 +3398,9 @@ int __kmem_cache_shrink(struct kmem_cache *s)
* list_lock. page->inuse here is the upper limit.
*/
list_for_each_entry_safe(page, t, &n->partial, lru) {
- list_move(&page->lru, slabs_by_inuse + page->inuse);
+ i = DIV_ROUND_UP(page->inuse * (SHRINK_BUCKETS - 1),
+ objects);
+ list_move(&page->lru, slabs_by_inuse + i);
if (!page->inuse)
n->nr_partial--;
}
@@ -3409,7 +3409,7 @@ int __kmem_cache_shrink(struct kmem_cache *s)
* Rebuild the partial list with the slabs filled up most
* first and the least used slabs at the end.
*/
- for (i = objects - 1; i > 0; i--)
+ for (i = SHRINK_BUCKETS - 1; i > 0; i--)
list_splice(slabs_by_inuse + i, n->partial.prev);
spin_unlock_irqrestore(&n->list_lock, flags);
@@ -3419,7 +3419,6 @@ int __kmem_cache_shrink(struct kmem_cache *s)
discard_slab(s, page);
}
- kfree(slabs_by_inuse);
return 0;
}
--
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