Re: [PATCH 0/6 v3] mm/memcontrol, page_counter: move stock from mem_cgroup to page_counter

[Joshua Hahn]

On Fri,  5 Jun 2026 08:35:56 -0700 Joshua Hahn <joshua.hahnjy@xxxxxxxxx> wrote:

> Memcg currently keeps a "stock" of 64 pages per-cpu to cache pre-charged
> allocations, allowing small allocations to avoid walking the expensive
> mem_cgroup hierarchy traversal and atomic operations on each charge.
> This design introduces a fastpath, but there is room for improvement:
> 
> 1. Currently, each CPU tracks up to 7 (NR_MEMCG_STOCK) mem_cgroups. When
>    more than 7 mem_cgroups are actively charging on a single CPU, a
>    random victim is evicted and its associated stock is drained.
> 
> 2. Stock management is tightly coupled to struct mem_cgroup, which makes
>    it difficult to add a new page_counter to mem_cgroup and have
>    multiple sources of stock management, which is required when trying
>    to introduce fastpaths to multiple hard limit checks.
> 
> This series moves the per-cpu stock down into the page_counter which
> consolidates stock limit checking and page_counter limit checking into
> page_counter_try_charge. This eliminates the 7-memcg-per-cpu slot limit,
> the random evictions (drain & refill), and slot traversal.

Sorry, two things that I forgot to add as reviewers' notes:
- There was a previous v3, but that was just a rebase, so I wasn't sure
  how to name that / this. I decided to name this one v3, since the
  last one didn't have any changes at all. I apologize in case there are
  any confusions.
- I think it is quite late in the merge cycle, this is intended for the
  next cycle, not this one.

Thank you!