mm: don't try THP alignment for FS without get_unmapped_area

Commit ed48e87c7df3 ("thp: add thp_get_unmapped_area_vmflags()") changes
thp_get_unmapped_area() to thp_get_unmapped_area_vmflags() in
__get_unmapped_area(), which doesn't initialize local get_area for
anonymous mappings.  This leads to us always trying THP alignment even for
file_operations which have a NULL ->get_unmapped_area() callback.

Since commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
boundaries") we only want to enable THP alignment for anonymous mappings,
so add a !file check to avoid attempting THP alignment for file mappings.

Found issue by code inspection.  THP alignment is used for easy or more
pmd mappings, from vma side.  This may cause unnecessary VMA fragmentation
and potentially worse performance on filesystems that do not actually
support THPs and thus cannot benefit from the alignment.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: ed48e87c7df3 ("thp: add thp_get_unmapped_area_vmflags()")
Signed-off-by: Kefeng Wang <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Rick Edgecombe <[email protected]>
Cc: Ryan Roberts <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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