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

[Thomas Hellstrom <thellstrom@vmware.com>]

Hi, Ralph,

On Fri, 2019-04-12 at 11:52 -0700, Ralph Campbell wrote:
> On 4/12/19 9:04 AM, Thomas Hellstrom wrote:
> > Add two utilities to a) write-protect and b) clean all ptes
> > pointing into
> > a range of an address space
> 
> A period at the end, please.
> 
> > 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.
> > 
> > The added file "apply_as_range.c" is initially listed as maintained
> > by
> > VMware under our DRM driver. If somebody would like it elsewhere,
> > that's of course no problem.
> > 
> > Notable changes since RFC:
> > - Added comments to help avoid the usage of these function for VMAs
> >    it's not intended for. We also do advisory checks on the
> > vm_flags and
> >    warn on illegal usage.
> > - Perform the pte modifications the same way softdirty does.
> > - Add mmu_notifier range invalidation calls.
> > - Add a config option so that this code is not unconditionally
> > included.
> > - Tell the mmu_gather code about pending tlb flushes.
> > 
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Matthew Wilcox <willy@infradead.org>
> > Cc: Will Deacon <will.deacon@arm.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Rik van Riel <riel@surriel.com>
> > Cc: Minchan Kim <minchan@kernel.org>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Huang Ying <ying.huang@intel.com>
> > Cc: Souptick Joarder <jrdr.linux@gmail.com>
> > Cc: "Jérôme Glisse" <jglisse@redhat.com>
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> 
> Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>

Thanks for reviewing the patches. I'll incorporate your suggestions in
v2.