First submitted an xfstest (generic/080) that demonstrates our current problem.
When run on ext4-dax mount, and I'd imagine Dave's xfs-dax mount this test
fails, on regular mount it works just fine.
then 2 patches to fix it.
The main problem is that current mm/memory.c will no call us with page_mkwrite
if we do not have an actual page mapping, which is what DAX uses.
The solution presented here introduces a new pfn_mkwrite to solve this problem.
Please see patch-2 for details.
I've been running with this patch for 4 month both HW and VMs with no apparent
danger, but see patch-2 I played it safe.
List of patches:
[PATCH 1/2] generic: 080 test that mmap-write updates c/mtime
This one is for Dave Chinner to submit to xfstests
[PATCH 1/2] mm: New pfn_mkwrite same as page_mkwrite for VM_PFNMAP
This patch I need help with please look into it?
[PATCH 2/2] dax: use pfn_mkwrite to update mtime
Please review and comment.