udmabuf: remove udmabuf_folio

udmabuf: remove udmabuf_folio

Currently, udmabuf handles folio by create an unpin list to record
each folio obtained from the list and unpinning them when released. To
maintain this, many struct have been established.

However, maintain this requires a significant amount of memory and
iter the list is a substantial overhead, which is not friendly to the
CPU cache.

When create, we arranged the folio array in the order of pin and set
the offset according to pgcnt. So, if record each pinned folio when
create, then can easy unpin it. Compare to use list to record it,
an array also can do this.

Hence, this patch setup a pinned_folios array(size is the pgcnt) to
instead of udmabuf_folio struct, it record each folio which pinned when
invoke memfd_pin_folios, then unpin folio by iter pinned_folios.

Note that, since a folio may be pinned multiple times, each folio can be
added to pinned_folios multiple times, depend on how many times the
folio has been pinned when create.

Compare to udmabuf_folio(24 byte size), a folio pointer is 8 byte, if no
large folio - each folio is PAGE_SIZE - and need to unpin when release.
So need to record each folio, by this patch, each folio can save 16 byte.

But if large folio used, depend on the large folio's number, the
pinned_folios array may take more memory, but it still can makes unpin
access more cache-friendly.

Signed-off-by: Huan Yang <link@vivo.com>
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240918025238.2957823-7-link@vivo.com