Re: [PATCH v8 0/7] mm/page_counter: move stock from mem_cgroup to page_counter

[Joshua Hahn]

On Thu, Nov 5, 2026 at 1:17 AM Balbir Singh <balbirs@xxxxxxxxxx> wrote:
>
> On Wed, Nov 04, 2026 at 03:30:21PM -0800, Joshua Hahn wrote:
> > INTRODUCTION
> > ============
> > Memcg keeps a per-CPU stock of precharged pages so that small and
> > frequent allocations do not walk the page_counter hierarchy every time.
> > Today, the stock implementation lives in memcontrol code, even though
> > the operation it caches is a page_counter charge. This makes it
> > difficult to add new page_counters to a memcg and preserve the fast path
> > behavior.
> >
> > This series moves the stock into the page_counter layer.
> > page_counter_try_charge() consumes the stock, charges a batch to the
> > hierarchy on a miss, and refills the stock with the surplus. Memcg no
> > longer manages the stock in try_charge_memcg.
> >
> > So the stock keeps the existing layout, which is still a per-CPU bank
> > of 7 slots, each holding a count of precharged pages that it hands out.
> > It maintains exclusion using local locks on each CPU, and for remote
> > drains we schedule on the memcg workqueue.
> >
> > This change gives us the following benefits:
> > - Separate charge caching (page_counter) from charge policy (memcg).
> > - Makes it simple to keep stock out of interior cgroups on cgroup v2.
> > - Prepares for future work for stock improvement, which can now be
> >   isolated from memcg changes.

[...snip...]

> Is the main motivation ease of addition of page_counters to a memcg?
> What would those counters be, why not add them here?

Hi Balbir,

Thank you for your interest in the series! So yes, that is the main
motivation but this series offers standalone benefits as well (which
are right above).

The new page_counters that I want to add track per-tier per-memcg
residence. Those are used for enforcement (and not necessarily for
visibility), so I think they wouldn't make too much sense to add on
their own now, without the actual enforcement parts.

What do you think? I've also linked my tiered memcg series [1] if you
wanted additional context.

Thank you, I hope you have a great day!
Joshua

[1] https://lore.kernel.org/all/20260807202059.2620949-1-joshua.hahnjy@xxxxxxxxx/