mm: compaction: update pageblock skip when first migration candidate is not at the start

isolate_migratepages_block should mark a pageblock as skip if scanning
started on an aligned pageblock boundary but it only updates the skip flag
if the first migration candidate is also aligned.  Tracing during a
compaction stress load (mmtests: workload-usemem-stress-numa-compact) that
many pageblocks are not marked skip causing excessive scanning of blocks
that had been recently checked.  Update pageblock skip based on
"valid_page" which is set if scanning started on a pageblock boundary.

[[email protected]: fix handling of skip bit]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mel Gorman <[email protected]>
Tested-by: Raghavendra K T <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Chuyi Zhou <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Maxim Levitsky <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Pedro Falcato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: gormanm

mm/compaction.c

@@ -392,18 +392,14 @@ void reset_isolation_suitable(pg_data_t *pgdat)
  * Sets the pageblock skip bit if it was clear. Note that this is a hint as
  * locks are not required for read/writers. Returns true if it was already set.
  */
-static bool test_and_set_skip(struct compact_control *cc, struct page *page,
-							unsigned long pfn)
+static bool test_and_set_skip(struct compact_control *cc, struct page *page)
 {
 	bool skip;
 
-	/* Do no update if skip hint is being ignored */
+	/* Do not update if skip hint is being ignored */
 	if (cc->ignore_skip_hint)
 		return false;
 
-	if (!pageblock_aligned(pfn))
-		return false;
-
 	skip = get_pageblock_skip(page);
 	if (!skip && !cc->no_set_skip_hint)
 		set_pageblock_skip(page);
@@ -470,8 +466,7 @@ static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 {
 }
 
-static bool test_and_set_skip(struct compact_control *cc, struct page *page,
-							unsigned long pfn)
+static bool test_and_set_skip(struct compact_control *cc, struct page *page)
 {
 	return false;
 }
@@ -1074,11 +1069,17 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 			lruvec_memcg_debug(lruvec, page_folio(page));
 
-			/* Try get exclusive access under lock */
-			if (!skip_updated) {
+			/*
+			 * Try get exclusive access under lock. If marked for
+			 * skip, the scan is aborted unless the current context
+			 * is a rescan to reach the end of the pageblock.
+			 */
+			if (!skip_updated && valid_page) {
 				skip_updated = true;
-				if (test_and_set_skip(cc, page, low_pfn))
+				if (test_and_set_skip(cc, valid_page) &&
+				    !cc->finish_pageblock) {
 					goto isolate_abort;
+				}
 			}
 
 			/*