Re: [RFCv3 PATCH 1/6] uacce: Add documents for WarpDrive/uacce

[Christopher Lameter]

On Mon, 19 Nov 2018, Jerome Glisse wrote:

> > IIRC this is solved in IB by automatically calling
> > madvise(MADV_DONTFORK) before creating the MR.
> >
> > MADV_DONTFORK
> >   .. This is useful to prevent copy-on-write semantics from changing the
> >   physical location of a page if the parent writes to it after a
> >   fork(2) ..
>
> This would work around the issue but this is not transparent ie
> range marked with DONTFORK no longer behave as expected from the
> application point of view.

Why would anyone expect a range registered via MR behave as normal? Device
I/O is going on into that range. Memory is already special.


> Also it relies on userspace doing the right thing (which is not
> something i usualy trust :)).

This has been established practice for 15 or so years in a couple of use
cases. Again user space already has to be doing special things in order to
handle RDMA is that area.