On Thu, Mar 21, 2013 at 02:13:38AM -0700, Roland Dreier wrote: > On Thu, Mar 21, 2013 at 1:51 AM, Michael S. Tsirkin <m...@redhat.com> wrote: > >> In that case, no, I don't see any reason for LOCAL_WRITE, since the > >> only RDMA operations that will access this memory are remote reads. > > > > What is the meaning of LOCAL_WRITE then? There are no local > > RDMA writes as far as I can see. > > Umm, it means you're giving the local adapter permission to write to > that memory. So you can use it as a receive buffer or as the target > for remote data from an RDMA read operation.
Well RDMA read has it's own flag, IB_ACCESS_REMOTE_READ. I don't see why do you need to give adapter permission to use memory as a receive buffer given that you must pass the address in the post receive verb, but maybe that's what the IB spec says so that's what the applications assumed? > > OK then what we need is a new flag saying "I really do not > > intend to write into this memory please do not break > > COW or do anything else just in case I do". > > Isn't that a shared read-only mapping? > > - R. Nothing to do with how the page is mapped. We can and do write the page before registration. BTW umem.c passes in force so it breaks COW even for read-only mappings, right? -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
