On Wed, May 05, 2021 at 11:29:54PM +0200, Vlastimil Babka wrote:

On 5/5/21 8:32 PM, Roman Gushchin wrote:

quoted

On Wed, May 05, 2021 at 08:02:06PM +0200, Vlastimil Babka wrote:

quoted

On 5/5/21 7:30 PM, Roman Gushchin wrote:

quoted

On Wed, May 05, 2021 at 11:46:13AM -0400, Waiman Long wrote:

quoted

With this change, all the objcg pointer array objects will come from
KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So
both the recursive kfree() problem and non-freeable slab problem are
gone. Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer
have mixed accounted and unaccounted objects, this will slightly reduce
the number of objcg pointer arrays that need to be allocated and save
a bit of memory.

Unfortunately the positive effect of this change will be likely
reversed by a lower utilization due to a larger number of caches.

Btw, I wonder if we also need a change in the slab caches merging procedure?
KMALLOC_NORMAL caches should not be merged with caches which can potentially
include accounted objects.

Good point. But looks like kmalloc* caches are extempt from all merging in
create_boot_cache() via

	s->refcount = -1;       /* Exempt from merging for now */

Wait, s->refcount is adjusted to 1 in create_kmalloc_cache() after calling
into create_boot_cache?

Hmm I missed that

Now I wonder why all kmalloc caches on my system have 0 aliases :)
cat /sys/kernel/slab/kmalloc-*/aliases

Yeah, I noticed it too, it's a good question. And I remember a case from
the past when it wasn't true (kmalloc-32 was shared with something else).