[PATCH v7 2/4] mm/compaction: enable compacting >0 order folios.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

migrate_pages() supports >0 order folio migration and during compaction,
even if compaction_alloc() cannot provide >0 order free pages,
migrate_pages() can split the source page and try to migrate the base
pages from the split.  It can be a baseline and start point for adding
support for compacting >0 order folios.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Huang Ying <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Adam Manzanares <a.manzanares@samsung.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yin Fengwei <fengwei.yin@intel.com>
---
 mm/compaction.c | 101 ++++++++++++++++++++++++++++++++++++------------
 1 file changed, 76 insertions(+), 25 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index ccd447282665..6509fab27be9 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -40,9 +40,22 @@ static inline void count_compact_events(enum vm_event_item item, long delta)
 {
 	count_vm_events(item, delta);
 }
+
+/*
+ * order == -1 is expected when compacting proactively via
+ * 1. /proc/sys/vm/compact_memory
+ * 2. /sys/devices/system/node/nodex/compact
+ * 3. /proc/sys/vm/compaction_proactiveness
+ */
+static inline bool is_via_compact_memory(int order)
+{
+	return order == -1;
+}
+
 #else
 #define count_compact_event(item) do { } while (0)
 #define count_compact_events(item, delta) do { } while (0)
+static inline bool is_via_compact_memory(int order) { return false; }
 #endif
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
@@ -816,6 +829,32 @@ static bool too_many_isolated(struct compact_control *cc)
 	return too_many;
 }
 
+/**
+ * skip_isolation_on_order() - determine when to skip folio isolation based on
+ *			       folio order and compaction target order
+ * @order:		to-be-isolated folio order
+ * @target_order:	compaction target order
+ *
+ * This avoids unnecessary folio isolations during compaction.
+ */
+static bool skip_isolation_on_order(int order, int target_order)
+{
+	/*
+	 * Unless we are performing global compaction (i.e.,
+	 * is_via_compact_memory), skip any folios that are larger than the
+	 * target order: we wouldn't be here if we'd have a free folio with
+	 * the desired target_order, so migrating this folio would likely fail
+	 * later.
+	 */
+	if (!is_via_compact_memory(target_order) && order >= target_order)
+		return true;
+	/*
+	 * We limit memory compaction to pageblocks and won't try
+	 * creating free blocks of memory that are larger than that.
+	 */
+	return order >= pageblock_order;
+}
+
 /**
  * isolate_migratepages_block() - isolate all migrate-able pages within
  *				  a single pageblock
@@ -947,7 +986,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			valid_page = page;
 		}
 
-		if (PageHuge(page) && cc->alloc_contig) {
+		if (PageHuge(page)) {
+			/*
+			 * skip hugetlbfs if we are not compacting for pages
+			 * bigger than its order. THPs and other compound pages
+			 * are handled below.
+			 */
+			if (!cc->alloc_contig) {
+				const unsigned int order = compound_order(page);
+
+				if (order <= MAX_PAGE_ORDER) {
+					low_pfn += (1UL << order) - 1;
+					nr_scanned += (1UL << order) - 1;
+				}
+				goto isolate_fail;
+			}
+			/* for alloc_contig case */
 			if (locked) {
 				unlock_page_lruvec_irqrestore(locked, flags);
 				locked = NULL;
@@ -1008,21 +1062,24 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		}
 
 		/*
-		 * Regardless of being on LRU, compound pages such as THP and
-		 * hugetlbfs are not to be compacted unless we are attempting
-		 * an allocation much larger than the huge page size (eg CMA).
-		 * We can potentially save a lot of iterations if we skip them
-		 * at once. The check is racy, but we can consider only valid
-		 * values and the only danger is skipping too much.
+		 * Regardless of being on LRU, compound pages such as THP
+		 * (hugetlbfs is handled above) are not to be compacted unless
+		 * we are attempting an allocation larger than the compound
+		 * page size. We can potentially save a lot of iterations if we
+		 * skip them at once. The check is racy, but we can consider
+		 * only valid values and the only danger is skipping too much.
 		 */
 		if (PageCompound(page) && !cc->alloc_contig) {
 			const unsigned int order = compound_order(page);
 
-			if (likely(order <= MAX_PAGE_ORDER)) {
-				low_pfn += (1UL << order) - 1;
-				nr_scanned += (1UL << order) - 1;
+			/* Skip based on page order and compaction target order. */
+			if (skip_isolation_on_order(order, cc->order)) {
+				if (order <= MAX_PAGE_ORDER) {
+					low_pfn += (1UL << order) - 1;
+					nr_scanned += (1UL << order) - 1;
+				}
+				goto isolate_fail;
 			}
-			goto isolate_fail;
 		}
 
 		/*
@@ -1165,10 +1222,11 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			}
 
 			/*
-			 * folio become large since the non-locked check,
-			 * and it's on LRU.
+			 * Check LRU folio order under the lock
 			 */
-			if (unlikely(folio_test_large(folio) && !cc->alloc_contig)) {
+			if (unlikely(skip_isolation_on_order(folio_order(folio),
+							     cc->order) &&
+				     !cc->alloc_contig)) {
 				low_pfn += folio_nr_pages(folio) - 1;
 				nr_scanned += folio_nr_pages(folio) - 1;
 				folio_set_lru(folio);
@@ -1788,6 +1846,10 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
 	struct compact_control *cc = (struct compact_control *)data;
 	struct folio *dst;
 
+	/* this makes migrate_pages() split the source page and retry */
+	if (folio_test_large(src))
+		return NULL;
+
 	if (list_empty(&cc->freepages)) {
 		isolate_freepages(cc);
 
@@ -2090,17 +2152,6 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
 	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
 }
 
-/*
- * order == -1 is expected when compacting proactively via
- * 1. /proc/sys/vm/compact_memory
- * 2. /sys/devices/system/node/nodex/compact
- * 3. /proc/sys/vm/compaction_proactiveness
- */
-static inline bool is_via_compact_memory(int order)
-{
-	return order == -1;
-}
-
 /*
  * Determine whether kswapd is (or recently was!) running on this node.
  *
-- 
2.43.0