block_invalidatepage(): only release page if the full page was invalidated

block_invalidatepage(): only release page if the full page was invalidated

Prior to commit d47992f86b30 ("mm: change invalidatepage prototype to
accept length"), an offset of 0 meant that the full page was being
invalidated.  After that commit, we need to instead check the length.

Jan said:
:
: The only possible issue is that try_to_release_page() was called more
: often than necessary.  Otherwise the issue is harmless but still it's good
: to have this fixed.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: d47992f86b307 ("mm: change invalidatepage prototype to accept length")
Signed-off-by: Jeff Moyer <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Lukas Czerner <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>