Re: [PATCH v3 09/16] sl[au]b: always get the cache from its page in kfree
From: Christoph Lameter <hidden>
Date: 2012-09-18 15:28:23
Also in:
linux-mm, lkml
On Tue, 18 Sep 2012, Glauber Costa wrote:
quoted hunk ↗ jump to hunk
index f2d760c..18de3f6 100644--- a/mm/slab.c +++ b/mm/slab.c@@ -3938,9 +3938,12 @@ EXPORT_SYMBOL(__kmalloc); * Free an object which was previously allocated from this * cache. */ -void kmem_cache_free(struct kmem_cache *cachep, void *objp) +void kmem_cache_free(struct kmem_cache *s, void *objp) { unsigned long flags; + struct kmem_cache *cachep = virt_to_cache(objp); + + VM_BUG_ON(!slab_equal_or_parent(cachep, s));
This is an extremely hot path of the kernel and you are adding significant processing. Check how the benchmarks are influenced by this change. virt_to_cache can be a bit expensive.
quoted hunk ↗ jump to hunk
diff --git a/mm/slub.c b/mm/slub.c index 4778548..a045dfc 100644 --- a/mm/slub.c +++ b/mm/slub.c@@ -2604,7 +2604,9 @@ void kmem_cache_free(struct kmem_cache *s, void *x) page = virt_to_head_page(x); - slab_free(s, page, x, _RET_IP_); + VM_BUG_ON(!slab_equal_or_parent(page->slab, s)); + + slab_free(page->slab, page, x, _RET_IP_);
Less of a problem here but you are eroding one advantage that slab has had in the past over slub in terms of freeing objects.