Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA

From: Jan Kara
Date: Tue Feb 12 2019 - 11:44:57 EST

On Tue 12-02-19 16:36:36, Christopher Lameter wrote:
> On Mon, 11 Feb 2019, Dan Williams wrote:
> > An mmap write after a fault due to a hole punch is free to trigger
> > SIGBUS if the subsequent page allocation fails. So no, I don't see
> > them as the same unless you're allowing for the holder of the MR to
> > receive a re-fault failure.
> Order 0 page allocation failures are generally not possible in that path.
> System will reclaim and OOM before that happens.

But also block allocation can fail in the filesystem or you can have memcgs
set up that make the page allocation fail, can't you? So in principle Dan
is right. Page faults can and do fail...

Jan Kara <jack@xxxxxxxx>