Re: [PATCH v6 10/14] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning

Jason Gunthorpe
2021-01-20T13:48:29Z

On Tue, Jan 19, 2021 at 08:43:29PM -0500, Pavel Tatashin wrote:
> +.. note::
> + Techniques that rely on long-term pinnings of memory (especially, RDMA and
> + vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
> + hot remove. Pinned pages cannot reside on ZONE_MOVABLE, to guarantee that
> + memory can still get hot removed - be aware that pinning can fail even if
> + there is plenty of free memory in ZONE_MOVABLE. In addition, using
> + ZONE_MOVABLE might make page pinning more expensive, because pages have to be
> + migrated off that zone first.

Just to point out, if anyone is using RDMA/etc with hotplug memory,
this series is likekly going to be a major regression for those users.

Jason