Re: [PATCH 00/16] The new slab memory controller

From: Michal Hocko
Date: Tue Oct 22 2019 - 09:31:52 EST

On Thu 17-10-19 17:28:04, Roman Gushchin wrote:
> This patchset provides a new implementation of the slab memory controller,
> which aims to reach a much better slab utilization by sharing slab pages
> between multiple memory cgroups. Below is the short description of the new
> design (more details in commit messages).
> Accounting is performed per-object instead of per-page. Slab-related
> vmstat counters are converted to bytes. Charging is performed on page-basis,
> with rounding up and remembering leftovers.
> Memcg ownership data is stored in a per-slab-page vector: for each slab page
> a vector of corresponding size is allocated. To keep slab memory reparenting
> working, instead of saving a pointer to the memory cgroup directly an
> intermediate object is used. It's simply a pointer to a memcg (which can be
> easily changed to the parent) with a built-in reference counter. This scheme
> allows to reparent all allocated objects without walking them over and changing
> memcg pointer to the parent.
> Instead of creating an individual set of kmem_caches for each memory cgroup,
> two global sets are used: the root set for non-accounted and root-cgroup
> allocations and the second set for all other allocations. This allows to
> simplify the lifetime management of individual kmem_caches: they are destroyed
> with root counterparts. It allows to remove a good amount of code and make
> things generally simpler.

What is the performance impact? Also what is the effect on the memory
reclaim side and the isolation. I would expect that mixing objects from
different cgroups would have a negative/unpredictable impact on the
memcg slab shrinking.
Michal Hocko