vmscan: isolate_lru_pages(): stop neighbour search if neighbour cannot be isolated

vmscan: isolate_lru_pages(): stop neighbour search if neighbour cannot be isolated

isolate_lru_pages() does not just isolate LRU tail pages, but also
isolates neighbour pages of the eviction page.  The neighbour search does
not stop even if neighbours cannot be isolated which is excessive as the
lumpy reclaim will no longer result in a successful higher order
allocation.  This patch stops the PFN neighbour pages if an isolation
fails and moves on to the next block.

Signed-off-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Wu Fengguang <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>