Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support

[Jason Gunthorpe]

On Thu, Jun 09, 2022 at 02:19:06PM +0100, Robin Murphy wrote:

> Is there a significant benefit to keeping both paths, or could we get away
> with just always using RCU? Realistically, pagetable pages aren't likely to
> be freed all that frequently, except perhaps at domain teardown, but that
> shouldn't really be performance-critical, and I guess we could stick an RCU
> sync point in iommu_domain_free() if we're really worried about releasing
> larger quantities of pages back to the allocator ASAP?

I think you are right, anything that uses the iommu_iotlb_gather may
as well use RCU too.

IIRC the allocators already know that RCU is often sitting on
freed-memory and have some contigency to flush it out before OOMing,
so nothing special should be needed.

Jason