On Thu, Mar 21, 2013 at 11:11:15AM -0600, Jason Gunthorpe wrote: > On Thu, Mar 21, 2013 at 11:39:47AM +0200, Michael S. Tsirkin wrote: > > 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 > > The access flags have to do with what independent access remote nodes > get. There are four major cases: > > access = IBV_ACCESS_REMOTE_READ says the adaptor will let remote nodes > read the memory. > > access = 0 (ie IBV_ACCESS_LOCAL_READ) says that only the adaptor, under > the direct control of the application, can read this memory. Remote > nodes are barred. > > access = IBV_ACCESS_REMOTE_WRITE|IBV_ACCESS_LOCAL_WRITE says the adaptor > will let remote nodes write the memory > > access = IBV_ACCESS_LOCAL_WRITE bars remote nodes from writing to that > memory. Only the adaptor, under the direct control of the application, > can write the memory. > > The fact LOCAL_READ/REMOTE_READ exists makes it possible to do what > you want - it guarentees the adaptor will never write to this memory > under any circumstances, so you can leave the page COW'd. If > LOCAL_WRITE was implied then you'd have to COW everything.. > > Would it be better to drive the COW break decision off the region's MM > flags? Ie if the memory is mapped read only into the process then you > can keep the COW at the RDMA layer, otherwise you should break > it. That seems more natural than a new flag? > > Jason
No because application does this: init page ... after a lot of time .. register send unregister so it can not be read only. -- 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/
