linux-kernel - [PATCH v3 1/3] mm/compaction: enable compacting >0 order folios.

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Date: Fri,  2 Feb 2024 11:15:52 -0500
From: Zi Yan <zi.yan@...t.com>
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Zi Yan <ziy@...dia.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	"Yin, Fengwei" <fengwei.yin@...el.com>,
	Yu Zhao <yuzhao@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Kemeng Shi <shikemeng@...weicloud.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Rohan Puri <rohan.puri15@...il.com>,
	Mcgrof Chamberlain <mcgrof@...nel.org>,
	Adam Manzanares <a.manzanares@...sung.com>,
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: [PATCH v3 1/3] mm/compaction: enable compacting >0 order folios.

From: Zi Yan <ziy@...dia.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.

Suggested-by: Huang Ying <ying.huang@...el.com>
Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/compaction.c | 43 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 35 insertions(+), 8 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 4add68d40e8d..e43e898d2c77 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -816,6 +816,21 @@ static bool too_many_isolated(struct compact_control *cc)
 	return too_many;
 }
 
+/*
+ * 1. if the page order is larger than or equal to target_order (i.e.,
+ * cc->order and when it is not -1 for global compaction), skip it since
+ * target_order already indicates no free page with larger than target_order
+ * exists and later migrating it will most likely fail;
+ *
+ * 2. compacting > pageblock_order pages does not improve memory fragmentation,
+ * skip them;
+ */
+static bool skip_isolation_on_order(int order, int target_order)
+{
+	return (target_order != -1 && order >= target_order) ||
+		order >= pageblock_order;
+}
+
 /**
  * isolate_migratepages_block() - isolate all migrate-able pages within
  *				  a single pageblock
@@ -1010,7 +1025,7 @@ 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).
+		 * 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.
@@ -1018,11 +1033,18 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		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
+			 * and skip hugetlbfs pages.
+			 */
+			if (skip_isolation_on_order(order, cc->order) ||
+			    PageHuge(page)) {
+				if (order <= MAX_PAGE_ORDER) {
+					low_pfn += (1UL << order) - 1;
+					nr_scanned += (1UL << order) - 1;
+				}
+				goto isolate_fail;
 			}
-			goto isolate_fail;
 		}
 
 		/*
@@ -1165,10 +1187,11 @@ 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);
@@ -1786,6 +1809,10 @@ 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) > 0)
+		return NULL;
+
 	if (list_empty(&cc->freepages)) {
 		isolate_freepages(cc);
 
-- 
2.43.0