On Tue, Apr 02, 2013 at 09:57:38AM -0700, Roland Dreier wrote: > On Tue, Apr 2, 2013 at 8:51 AM, Michael S. Tsirkin <m...@redhat.com> wrote: > >> At the moment registering an MR breaks COW. This breaks memory > >> overcommit for users such as KVM: we have a lot of COW pages, e.g. > >> instances of the zero page or pages shared using KSM. > >> > >> If the application does not care that adapter sees stale data (for > >> example, it tracks writes reregisters and resends), it can use a new > >> IBV_ACCESS_GIFT flag to prevent registration from breaking COW. > >> > >> The semantics are similar to that of SPLICE_F_GIFT thus the name. > >> > >> Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > > > > Roland, Michael is yet to test this but could you please > > confirm whether this looks acceptable to you? > > The patch itself is reasonable I guess, given the needs of this particular > app. > > I'm not particularly happy with the name of the flag. The analogy > with SPLICE_F_GIFT doesn't seem particularly strong and I'm not > convinced even the splice flag name is very understandable. But in > the RDMA case there's not really any sense in which we're "gifting" > memory to the adapter -- we're just telling the library "please don't > trigger copy-on-write" and it doesn't seem particularly easy for users > to understand that from the flag name. > > - R.
The point really is that any writes by application won't be seen until re-registration, right? OK, what's a better name? IBV_ACCESS_NON_COHERENT? Please tell me what is preferable and we'll go ahead with it. -- 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/
