On Wed, May 08, 2024 at 12:35:52PM +0100, Pavel Begunkov wrote:

quoted

all these, because e.g. ttm internally does have a page pool because
depending upon allocator, that's indeed beneficial. Other drm drivers have
more buffer-based concepts for opportunistically memory around, usually
by marking buffers that are just kept as cache as purgeable (which is a
concept that goes all the way to opengl/vulkan).

Because in this case it solves nothing and helps with nothing, quite
the opposite. Just as well we can ask why NVMe doesn't wrap user pages
into a dmabuf while doing IO.

You seem to confused totally unrelated things.

For short-term pins, that is pin_user_pages without FOLL_LONGTERM there
would never be any point in using a dmabuf as the pin is transient.  For
long-term pin dmabufs in the block layer absolutely make sense, and I
wish io_uring would have just implemented them from the start instead of
the current fixed buffers that are not quite as useful by not
pre-mapping DMA and not supporting P2P.