filemap: allocate mapping_min_order folios in the page cache

filemap_create_folio() and do_read_cache_folio() were always allocating
folio of order 0. __filemap_get_folio was trying to allocate higher
order folios when fgp_flags had higher order hint set but it will default
to order 0 folio if higher order memory allocation fails.

Supporting mapping_min_order implies that we guarantee each folio in the
page cache has at least an order of mapping_min_order. When adding new
folios to the page cache we must also ensure the index used is aligned to
the mapping_min_order as the page cache requires the index to be aligned
to the order of the folio.

Co-developed-by: Luis Chamberlain <[email protected]>
Signed-off-by: Luis Chamberlain <[email protected]>
Signed-off-by: Pankaj Raghav <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Tested-by: David Howells <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Daniel Gomez <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

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