Re: [PATCH 6/6] userfaultfd: collapse VM_UFFD_{MISSING,WP,MINOR,RWP} into single VM_UFFD

On Thu, Aug 27, 2026 at 05:19:30PM +0200, David Hildenbrand (Arm) wrote:

On 8/27/26 13:18, Lorenzo Stoakes (ARM) wrote:

quoted

On Thu, Aug 27, 2026 at 12:16:32PM +0100, Lorenzo Stoakes (ARM) wrote:

quoted

So actually you're increasing by a cacheline and increasing the VMA size by
64 bytes, i.e. 1/3, which is unacceptable obviously.

Maybe there's something that can be done with:

		/* forced alignments: 1 */

Perhaps? But that looks potentially ugly.

I say elsewhere (or think I do) but to highlight - I think probably we could fix
this by putting the flags in the low bits of vm_uffd_state.ctx?

if that's possible that would be clearly preferable memory-wise.

This gives only 4 bits and makes this completely not extendable.

So I think I'll drop this for now and wait until VMA grows another cache
line or until having per-VMA uffd state rather than a pointer to per-fd
context is a must.
 

-- 
Cheers,

David

-- 
Sincerely yours,
Mike.