Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap via MREMAP_RELOCATE_ANON

[Lorenzo Stoakes]

OK have dug into this some more with a drgn script to read actual kernel
metadata state and it's simpler than I thought - the root anon_vma is
self-childed, but descendent anon_vma's are not.

We can correct this with a anon_vma->root == anon_vma check. I believe
we're probably safe with anon_vma reuse, because in that instance the
anon_vma would not be mapped a shared folio.

However, to be safe, I will check this, and I as I said previously, I will
add a number of tests explicitly tested forking scenarios.

The respin should have this fully addressed.

Thanks, Lorenzo