mm/memory: add vm_normal_folio()

mm/memory: add vm_normal_folio()

Patch series "Convert deactivate_page() to folio_deactivate()", v4.

Deactivate_page() has already been converted to use folios.  This patch
series modifies the callers of deactivate_page() to use folios.  It also
introduces vm_normal_folio() to assist with folio conversions, and
converts deactivate_page() to folio_deactivate() which takes in a folio.

This patch (of 4):

Introduce a wrapper function called vm_normal_folio().  This function
calls vm_normal_page() and returns the folio of the page found, or null if
no page is found.

This function allows callers to get a folio from a pte, which will
eventually allow them to completely replace their struct page variables
with struct folio instead.

Link: https://lkml.kernel.org/r/20221221180848.20774-1-vishal.moola@gmail.com
Link: https://lkml.kernel.org/r/20221221180848.20774-2-vishal.moola@gmail.com
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>