mm: Handle per-folio private data

Add folio_get_private() which mirrors page_private() -- ie folio private
data is the same as page private data.  The only difference is that these
return a void * instead of an unsigned long, which matches the majority
of users.

Turn attach_page_private() into folio_attach_private() and reimplement
attach_page_private() as a wrapper.  No filesystem which uses page private
data currently supports compound pages, so we're free to define the rules.
attach_page_private() may only be called on a head page; if you want
to add private data to a tail page, you can call set_page_private()
directly (and shouldn't increment the page refcount!  That should be
done when adding private data to the head page / folio).

This saves 813 bytes of text with the distro-derived config that I'm
testing due to removing the calls to compound_head() in get_page()
& put_page().

Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: Jeff Layton <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Reviewed-by: William Kucharski <[email protected]>
Reviewed-by: David Howells <[email protected]>
Acked-by: Mike Rapoport <[email protected]>

0 files changed, 0 insertions, 0 deletions