Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb)

On Tue 21-12-21 19:59:16, Jason Gunthorpe wrote:

On Tue, Dec 21, 2021 at 06:40:30PM +0100, David Hildenbrand wrote:

...

What adds complexity to correctly maintain the "exclusive" state are at least:

• KSM (might be harder, have to think about it)

I know little about it, but isn't KSM like fork where it is trying to WP pages with the intention of copying them? Shouldn't KSM completely reject WP'ing a page that is under any kind of writable GUP?

I know little about KSM as well but I think fundamentally it has similar requirements for anon pages as filesystems have for page cache pages e.g. when doing block deduplication or data checksumming... I.e., it needs to make sure data in the page is stable and nobody can modify it.

Honza