mm/compaction: reduce the difference between low and high watermarks

mm/compaction: reduce the difference between low and high watermarks

Reduce the diff between low and high watermarks when compaction
proactiveness is set to high.  This allows users who set the proactiveness
really high to have more stable fragmentation score over time.

Link: https://lkml.kernel.org/r/20250404111103.1994507-3-mclapinski@google.com
Signed-off-by: Michal Clapinski <mclapinski@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>