On 2020-02-27 10:17 a.m., Jason Gunthorpe wrote: >> Instead of this, this series proposes a change to arch_add_memory() >> to take the pgprot required by the mapping which allows us to >> explicitly set pagetable entries for P2PDMA memory to WC. > > Is there a particular reason why WC was selected here? I thought for > the p2pdma cases there was no kernel user that touched the memory? Yes, that's correct. I choose WC here because the existing users are registering memory blocks without side effects which fit the WC semantics well. > I definitely forsee devices where we want UC instead. Yes. My expectation is that once we have a kernel user that needs this, we'd wire the option through struct dev_pagemap so the caller can choose the mapping that makes sense. Logan
