mm: page_alloc: allowing mTHP compaction to capture the freed page directly

Currently, compaction_capture() does not allow lower-order allocations to
directly capture the movable free pages, even though lower-order
allocations might also be requesting movable pages, that can lead to more
compaction scanning.  And, with the enablement of mTHP, such situations
will become more common.

Thus allowing lower-order (mTHP) allocations of movable page types
directly capture the movable free pages can avoid unnecessary compaction
scanning, meanwhile that won't pollute the movable pageblock.  With
testing 1M mTHP compaction, it can be seen that compaction scanning is
significantly reduced.

                                   mm-unstable       patched
Ops Compaction pages isolated      116598741.00   120946702.00
Ops Compaction migrate scanned    1764870054.00  1488621550.00
Ops Compaction free scanned       7707879039.00  4986299318.00
Ops Compact scan efficiency               22.90          29.85
Ops Compaction cost                    73797.69       72933.48

Link: https://lkml.kernel.org/r/8118a5d66a034736a48433beddaca60ed78577c4.1712892329.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -595,12 +595,14 @@ compaction_capture(struct capture_control *capc, struct page *page,
 		return false;
 
 	/*
-	 * Do not let lower order allocations pollute a movable pageblock.
+	 * Do not let lower order allocations pollute a movable pageblock
+	 * unless compaction is also requesting movable pages.
 	 * This might let an unmovable request use a reclaimable pageblock
 	 * and vice-versa but no more than normal fallback logic which can
 	 * have trouble finding a high-order free page.
 	 */
-	if (order < pageblock_order && migratetype == MIGRATE_MOVABLE)
+	if (order < pageblock_order && migratetype == MIGRATE_MOVABLE &&
+	    capc->cc->migratetype != MIGRATE_MOVABLE)
 		return false;
 
 	capc->page = page;