Re: [PATCH 2/3] dax: stop using VM_MIXEDMAP for dax

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Sep 28, 2017 at 9:32 AM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Dan Williams <dan.j.williams@intel.com> 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.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>