On Thu, Sep 28, 2017 at 9:32 AM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > Dan Williams <dan.j.williams@xxxxxxxxx> writes: > >> Now that we always have pages for DAX we can stop setting VM_MIXEDMAP. >> This does require some small fixups for the pte insert routines that dax >> utilizes. > > It used to be that userspace would look to see if it had a 'mm' entry in > /proc/pid/smaps to determine whether or not it got a direct mapping. > Later, that same userspace (nvml) just uniformly declared dax not > available from any Linux file system, since msync was required. And, I > guess DAX has always been marked experimental, so the interface can be > changed. > > All this is to say I guess it's fine to change this. Yes, it was always broken / dangerous to look for 'mm' as a pseudo-dax flag. >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 680506faceae..d682f60670ff 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -1111,7 +1111,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm, >> * We later require that vma->vm_flags == vm_flags, >> * so this tests vma->vm_flags & VM_SPECIAL, too. >> */ >> - if (vm_flags & VM_SPECIAL) >> + if ((vm_flags & VM_SPECIAL)) >> return NULL; > > That looks superfluous. Whoops, yeah. That was a case where I converted it to add a vma_is_dax() check and then decided we don't need that.
