mm: clarify __GFP_NOFAIL deprecation status

mm: clarify __GFP_NOFAIL deprecation status

__GFP_NOFAIL is documented as a deprecated flag since commit
478352e789f5 ("mm: add comment about deprecation of __GFP_NOFAIL").

This has discouraged people from using it but in some cases an opencoded
endless loop around allocator has been used instead.  So the allocator
is not aware of the de facto __GFP_NOFAIL allocation because this
information was not communicated properly.

Let's make clear that if the allocation context really cannot afford
failure because there is no good failure policy then using __GFP_NOFAIL
is preferable to opencoding the loop outside of the allocator.

[[email protected]: coding-style fixes]
Signed-off-by: Michal Hocko <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Vipul Pandya <[email protected]>
Cc: Jan Kara <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>