[PATCH 3/4] mm: compaction: Update pageblock skip when first migration candidate is not at the start

[Mel Gorman <mgorman@techsingularity.net>]

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.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/compaction.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index accc6568091a..d7be990b1d60 100644
--- a/mm/compaction.c
+++ b/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;
 }
@@ -1075,9 +1070,9 @@ 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) {
+			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))
 					goto isolate_abort;
 			}
 
-- 
2.35.3