On Mon, Jan 27, 2020 at 09:34:46AM -0800, Roman Gushchin wrote: > This is fairly big but mostly red patch, which makes all non-root > slab allocations use a single set of kmem_caches instead of > creating a separate set for each memory cgroup. > > Because the number of non-root kmem_caches is now capped by the number > of root kmem_caches, there is no need to shrink or destroy them > prematurely. They can be perfectly destroyed together with their > root counterparts. This allows to dramatically simplify the > management of non-root kmem_caches and delete a ton of code. This is definitely going in the right direction. But it doesn't quite explain why we still need two sets of kmem_caches? In the old scheme, we had completely separate per-cgroup caches with separate slab pages. If a cgrouped process wanted to allocate a slab object, we'd go to the root cache and used the cgroup id to look up the right cgroup cache. On slab free we'd use page->slab_cache. Now we have slab pages that have a page->objcg array. Why can't all allocations go through a single set of kmem caches? If an allocation is coming from a cgroup and the slab page the allocator wants to use doesn't have an objcg array yet, we can allocate it on the fly, no?
