Re: [RFC PATCH] dma-buf: add a generic reclaim-priority hint

[Ferran Duarri]

Thanks, and the FOLL_LONGTERM framing was my error - I should've checked it
before I wrote it. I'd been treating the pin as an accounting detail rather
than the thing that makes the buffer un-migratable, and once you look at
check_and_migrate_movable_pages_or_folios() and what CMA does around it,
that's obviously not a premise to build UAPI on.

On the in-tree user, that's fair. I said much the same in a follow-up on the
20th which you may not have seen - there isn't one, the only consumer is my
own out-of-tree module, and that isn't a reason to take UAPI.

One thing I'd like to understand before dropping it. You mention the
exporter migrating a buffer between local memory, system memory and swap.
If this ever did get an in-tree consumer, is that the shape you'd expect -
something on dma_buf_ops the exporter implements, rather than a hint field
plus an ioctl? I'd rather hear the direction is wrong than come back later
with the same idea in different clothes.

Cheers,
Ferran