Re: [PATCH] arm64: Increase the max granular size

Catalin Marinas
2015-11-04T15:39:18Z

On Wed, Nov 04, 2015 at 09:28:34AM -0600, Christoph Lameter wrote:
> On Wed, 4 Nov 2015, Catalin Marinas wrote:
>
> > BTW, assuming L1_CACHE_BYTES is 512 (I don't ever see this happening but
> > just in theory), we potentially have the same issue. What would save us
> > is that INDEX_NODE would match the first "kmalloc-512" cache, so we have
> > it pre-populated.
>
> Ok maybe add some BUILD_BUG_ONs to ensure that builds fail until we have
> addressed that.

A BUILD_BUG_ON should be fine.

Thinking some more, I think if KMALLOC_MIN_SIZE is 128, there is no gain
with off-slab management since the freelist allocation would still be
128 bytes. An alternative to reverting while still having a little
benefit of off-slab for 256 bytes objects (rather than 512 as we would
get with the revert):

diff --git a/mm/slab.c b/mm/slab.c
index 4fcc5dd8d5a6..ac32b4a0f2ec 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2212,8 +2212,8 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
* it too early on. Always use on-slab management when
* SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak)
*/
- if ((size >= (PAGE_SIZE >> 5)) && !slab_early_init &&
- !(flags & SLAB_NOLEAKTRACE))
+ if ((size >= (PAGE_SIZE >> 5)) && (size > KMALLOC_MIN_SIZE) &&
+ !slab_early_init && !(flags & SLAB_NOLEAKTRACE))
/*
* Size is large, assume best to place the slab management obj
* off-slab (should allow better packing of objs).

Whichever you prefer.

--
Catalin