Re: [PATCH 00/11] mm/cma: charge cma allocation to memcg using per area counters

On Wed, Aug 26, 2026 at 10:04:27AM +0200, Michal Hocko wrote:

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You cannot really assume usecase, requirements, lifetime etc. for an
arbitrary cma area. I do not think this is a viable way forward. Focus
on your real usecase, which seems to be dmabufs.

While dmabufs are indeed my main use case, they are quite generic and
may not always have system memory backing them (device memory). Working
at the CMA allocator alleviated these disparities.

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Explain what do you want to achieve and then we can think whether memcg
is the right model for that usecase

Hopefully I expressed this in a better way by now. In short, enforce
usage limits for concurrent CMA users using shared CMA resources.

Thanks. Yes this is more clear now. And it resembles hugetlb situation
more than memcg. You simply need a memory pool specific access and usage
control. Dispersing that to a global memcg limit seems rather coarse and 
I would say impractical. So it really calls for a per pool control with
an understanding of how the specific pool really works.

I'm not entirely sure what you meant there, but I think we also need to
have it account in a "global" limit somewhere. Which CMA pool is backing
a CMA device allocation is pretty unpredictable and unstable across
boots, so if userspace wants to put meaningful limits somewhat
generically, we'll need some kind of catchall limit.

Maxime