khugepaged: inline hpage_collapse_alloc_folio()

khugepaged: inline hpage_collapse_alloc_folio()

Patch series "khugepaged folio conversions".

We've been kind of hacking piecemeal at converting khugepaged to use
folios instead of compound pages, and so this patchset is a little larger
than it should be as I undo some of our wrong moves in the past.  In
particular, collapse_file() now consistently uses 'new_folio' for the
freshly allocated folio and 'folio' for the one that's currently in use.

This patch (of 7):

This function has one caller, and the combined function is simpler to
read, reason about and modify.

Link: https://lkml.kernel.org/r/20240403171838.1445826-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240403171838.1445826-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>