[PATCH 1/2] mm: compaction: consider the number of scanning compound pages in isolate fail path

[Baolin Wang]

The commit b717d6b93b54 ("mm: compaction: include compound page count
for scanning in pageblock isolation") had added compound page statistics
for scanning in pageblock isolation, to make sure the number of scanned
pages are always larger than the number of isolated pages when isolating
mirgratable or free pageblock.

However, when failed to isolate the pages when scanning the mirgratable or
free pageblock, the isolation failure path did not consider the scanning
statistics of the compound pages, which can show the incorrect number of
scanned pages in tracepoints or the vmstats to make people confusing about
the page scanning pressure in memory compaction.

Thus we should take into account the number of scanning pages when failed
to isolate the compound pages to make the statistics accurate.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/compaction.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 5a9501e0ae01..c9d9ad958e2a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -587,6 +587,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 				blockpfn += (1UL << order) - 1;
 				cursor += (1UL << order) - 1;
 			}
+			nr_scanned += (1UL << order) - 1;
 			goto isolate_fail;
 		}
 
@@ -873,9 +874,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			cond_resched();
 		}
 
-		nr_scanned++;
-
 		page = pfn_to_page(low_pfn);
+		nr_scanned += compound_nr(page);
 
 		/*
 		 * Check if the pageblock has already been marked skipped.
@@ -1077,6 +1077,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			 */
 			if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
 				low_pfn += compound_nr(page) - 1;
+				nr_scanned += compound_nr(page) - 1;
 				SetPageLRU(page);
 				goto isolate_fail_put;
 			}
@@ -1097,7 +1098,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 isolate_success_no_list:
 		cc->nr_migratepages += compound_nr(page);
 		nr_isolated += compound_nr(page);
-		nr_scanned += compound_nr(page) - 1;
 
 		/*
 		 * Avoid isolating too much unless this block is being
-- 
2.27.0