linux-kernel - [RFC PATCH v2 2/7] mm: compaction: handle non-lru compound pages properly in isolate_migratepages

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Date:   Thu,  9 Dec 2021 18:04:09 -0500
From:   Zi Yan <zi.yan@...t.com>
To:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>, Zi Yan <ziy@...dia.com>
Subject: [RFC PATCH v2 2/7] mm: compaction: handle non-lru compound pages properly in isolate_migratepages_block().

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

In isolate_migratepages_block(), a !PageLRU tail page can be encountered
when the page is larger than a pageblock. Use compound head page for the
checks inside and skip the entire compound page when isolation succeeds.

Signed-off-by: Zi Yan <ziy@...dia.com>
---
 mm/compaction.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index b4e94cda3019..ad9053fbbe06 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -979,19 +979,23 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		 * Skip any other type of page
 		 */
 		if (!PageLRU(page)) {
+			struct page *head = compound_head(page);
 			/*
 			 * __PageMovable can return false positive so we need
 			 * to verify it under page_lock.
 			 */
-			if (unlikely(__PageMovable(page)) &&
-					!PageIsolated(page)) {
+			if (unlikely(__PageMovable(head)) &&
+					!PageIsolated(head)) {
 				if (locked) {
 					unlock_page_lruvec_irqrestore(locked, flags);
 					locked = NULL;
 				}
 
-				if (!isolate_movable_page(page, isolate_mode))
+				if (!isolate_movable_page(head, isolate_mode)) {
+					low_pfn += (1 << compound_order(head)) - 1 - (page - head);
+					page = head;
 					goto isolate_success;
+				}
 			}
 
 			goto isolate_fail;
-- 
2.33.0