Re: [PATCH 0/6] RFC v2: mm: gup/dma tracking

[Christopher Lameter]

On Mon, 4 Feb 2019, Ira Weiny wrote:

> On Mon, Feb 04, 2019 at 05:14:19PM +0000, Christopher Lameter wrote:
> > Frankly I still think this does not solve anything.
> >
> > Concurrent write access from two sources to a single page is simply wrong.
> > You cannot make this right by allowing long term RDMA pins in a filesystem
> > and thus the filesystem can never update part of its files on disk.
> >
> > Can we just disable RDMA to regular filesystems? Regular filesystems
> > should have full control of the write back and dirty status of their
> > pages.
>
> That may be a solution to the corruption/crashes but it is not a solution which
> users want to see.  RDMA directly to file systems (specifically DAX) is a use
> case we have seen customers ask for.

DAX is a special file system that does not use writeback for the DAX
mappings. Thus it could be an exception. And the pages are already pinned.