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    SubjectRe: [PATCHv2] rdma: add a new IB_ACCESS_GIFT flag
    On Tue, Apr 02, 2013 at 08:05:21PM +0300, Michael S. Tsirkin wrote:
    > 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 <mst@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 <mst@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.

    Um. ping? We are at -rc5 and things need to fall into place
    if we are to have it in 3.10 ...

    > --
    > MST


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