On Wed, Dec 19, 2018 at 12:35:40PM +0100, Jan Kara wrote: > On Wed 19-12-18 21:28:25, Dave Chinner wrote: > > On Tue, Dec 18, 2018 at 08:03:29PM -0700, Jason Gunthorpe wrote: > > > On Wed, Dec 19, 2018 at 10:42:54AM +1100, Dave Chinner wrote: > > > > > > > Essentially, what we are talking about is how to handle broken > > > > hardware. I say we should just brun it with napalm and thermite > > > > (i.e. taint the kernel with "unsupportable hardware") and force > > > > wait_for_stable_page() to trigger when there are GUP mappings if > > > > the underlying storage doesn't already require it. > > > > > > If you want to ban O_DIRECT/etc from writing to file backed pages, > > > then just do it. > > > > O_DIRECT IO *isn't the problem*. > > That is not true. O_DIRECT IO is a problem. In some aspects it is > easier than the problem with RDMA but currently O_DIRECT IO can > crash your machine or corrupt data the same way RDMA can. Just the > race window is much smaller. So we have to fix the generic GUP > infrastructure to make O_DIRECT IO work. I agree that fixing RDMA > will likely require even more work like revokable leases or what > not. This is what I've understood, talking to all the experts. Dave? Why do you think O_DIRECT is actually OK? I agree the duration issue with RDMA is different, but don't forget, O_DIRECT goes out to the network too and has potentially very long timeouts as well. If O_DIRECT works fine then lets use the same approach in RDMA?? Jason
