https://kernelnewbies.org/MatthewWilcox/Memdescs In the short term, we're removing page->mapping, ->index, ->lru and ->memcg_data, leaving ->flags, ->_refcount and ->private as well as the newly-introduced ->memdesc. So if all you needed to do was identify which pages belong to you, I'd suggest setting ->private to a unique value (eg bdev->dev_mapping). But it feels like you need more than that; you need a refcount, and you need to map pages to userspace. Do you need to support GUP on these pages (ie can it be the user buffer for O_DIRECT, can it be registered with RDMA, that kind of thing), or is this memory just for userspace to do load/store, and no fancy stuff is allowed? At this point, I'd suggest that you allocate folios rather than pages. That lets us continue to use folio->mapping to distinguish these pages. There would be an opportunity to save some memory in the future by using a slimmer control structure once we understand the new system better, but maybe it's OK to just keep using a folio forever. Thoughts?
