mm: add find_lock_head

mm: add find_lock_head

Add a new FGP_HEAD flag which avoids calling find_subpage() and add a
convenience wrapper for it.

Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: William Kucharski <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>