[PATCH] mm/compaction: count pages and stop correctly during page isolation.

[Zi Yan]

From: Zi Yan <z...@nvidia.com>

In isolate_migratepages_block, when cc->alloc_contig is true, we are
able to isolate compound pages, nr_migratepages and nr_isolated did not
count compound pages correctly, causing us to isolate more pages than we
thought. Use thp_nr_pages to count pages. Otherwise, we might be trapped
in too_many_isolated while loop, since the actual isolated pages can go
up to COMPACT_CLUSTER_MAX*512=16384, where COMPACT_CLUSTER_MAX is 32,
since we stop isolation after cc->nr_migratepages reaches to
COMPACT_CLUSTER_MAX.

In addition, after we fix the issue above, cc->nr_migratepages could
never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated,
thus page isolation could not stop as we intended. Change the isolation
stop condition to >=.

Signed-off-by: Zi Yan <z...@nvidia.com>
---
 mm/compaction.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index ee1f8439369e..0683a4999581 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1012,8 +1012,8 @@ isolate_migratepages_block(struct compact_control *cc, 
unsigned long low_pfn,
 
 isolate_success:
                list_add(&page->lru, &cc->migratepages);
-               cc->nr_migratepages++;
-               nr_isolated++;
+               cc->nr_migratepages += thp_nr_pages(page);
+               nr_isolated += thp_nr_pages(page);
 
                /*
                 * Avoid isolating too much unless this block is being
@@ -1021,7 +1021,7 @@ isolate_migratepages_block(struct compact_control *cc, 
unsigned long low_pfn,
                 * or a lock is contended. For contention, isolate quickly to
                 * potentially remove one source of contention.
                 */
-               if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
+               if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
                    !cc->rescan && !cc->contended) {
                        ++low_pfn;
                        break;
@@ -1132,7 +1132,7 @@ isolate_migratepages_range(struct compact_control *cc, 
unsigned long start_pfn,
                if (!pfn)
                        break;
 
-               if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
+               if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
                        break;
        }
 
-- 
2.28.0