Re: [PATCH v3 2/2] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches

[Roman Gushchin]

On Wed, May 05, 2021 at 08:02:06PM +0200, Vlastimil Babka wrote:
> On 5/5/21 7:30 PM, Roman Gushchin wrote:
> > On Wed, May 05, 2021 at 11:46:13AM -0400, Waiman Long wrote:
> >> 
> >> 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?

It means they are not exempt actually.