mm: vmscan: reclaim highmem zone if buffer_heads is over limit

mm: vmscan: reclaim highmem zone if buffer_heads is over limit

We have been reclaimed highmem zone if buffer_heads is over limit but
commit 6b4f7799c6a5 ("mm: vmscan: invoke slab shrinkers from
shrink_zone()") changed the behavior so it doesn't reclaim highmem zone
although buffer_heads is over the limit.  This patch restores the logic.

Fixes: 6b4f7799c6a5 ("mm: vmscan: invoke slab shrinkers from shrink_zone()")
Signed-off-by: Minchan Kim <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>