Re: [PATCH v5 3/9] mm: Add write-protect and clean utilities for address space ranges

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 12, 2019 at 08:42:37AM +0200, Thomas Hellström (VMware) wrote:
> From: Thomas Hellstrom <thellstrom@vmware.com>
> 
> Add two utilities to a) write-protect and b) clean all ptes pointing into
> a range of an address space.
> The utilities are intended to aid in tracking dirty pages (either
> driver-allocated system memory or pci device memory).
> The write-protect utility should be used in conjunction with
> page_mkwrite() and pfn_mkwrite() to trigger write page-faults on page
> accesses. Typically one would want to use this on sparse accesses into
> large memory regions. The clean utility should be used to utilize
> hardware dirtying functionality and avoid the overhead of page-faults,
> typically on large accesses into small memory regions.

Please use EXPORT_SYMBOL_GPL, just like for apply_to_page_range and
friends.  Also in general new core functionality like this should go
along with the actual user, we don't need to repeat the hmm disaster.