Re: [PATCH rdma-next v2 0/3] cgroup/rdma: add MR memory size resource tracking

["Michal Koutný" <mkoutny@suse.com>]

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Hi.

On Fri, May 29, 2026 at 05:07:30PM +0800, Tao Cui <cui.tao@linux.dev> wrote:
> The real scarce resource in multi-tenant
> deployments is pinned memory: how much physical memory gets registered
> through MRs.
> ...
> 3. Overlap with memory cgroup: mr_mem does not count process memory
>    usage; it represents a per-device DMA registration budget: the
>    amount of memory this cgroup may register through a given HCA.
>    This is a different dimension from what memory cgroup tracks.  An
>    administrator might set mr_mem limits differently per device, which
>    memory cgroup cannot express.
> 
>    In particular, mr_mem tracks the registered memory range associated
>    with the MR rather than exact dynamically pinned pages (e.g. for
>    ODP MRs).  This is a stable, policy-oriented approximation of
>    registration footprint, not an attempt at precise physical page
>    accounting.

IIUC the pinned memory is regular RAM, i.e. it could be controlled with
memcg as needed. Or is there "physical" limit of what can be assigned to
a single device?

BTW, have a look at [1], it'd be good to converge to similar approach
(the current proposal allows distinguishing whether charging should
include or exempt memcg counting). Also it seems, that the dmem
controller could be a one-stop solution for all DMA charges. Please tell
me if there are any distinguishing factors between RDMA devices' memory
and these dmem memory regions.

Thanks,
Michal


[1] https://lore.kernel.org/r/20260519-cgroup-dmem-memcg-double-charge-v2-0-db4d1407062b@redhat.com/

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