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

From: Christopher Lameter
Date: Fri Feb 15 2019 - 13:31:41 EST

On Fri, 15 Feb 2019, Matthew Wilcox wrote:

> > Since RDMA is something similar: Can we say that a file that is used for
> > RDMA should not use the page cache?
> That makes no sense. The page cache is the standard synchronisation point
> for filesystems and processes. The only problems come in for the things
> which bypass the page cache like O_DIRECT and DAX.

It makes a lot of sense since the filesystems play COW etc games with the
pages and RDMA is very much like O_DIRECT in that the pages are modified
directly under I/O. It also bypasses the page cache in case you have
not noticed yet.

Both filesysetms and RDMA acting on a page cache at
the same time lead to the mess that we are trying to solve.