Re: [RFC PATCH v3 2/8] mm: compaction: handle non-lru compound pages properly in isolate_migratepages_block().

On 13 Jan 2022, at 9:57, Zi Yan wrote:

On 12 Jan 2022, at 6:01, David Hildenbrand wrote:

quoted

On 05.01.22 22:47, Zi Yan wrote:

quoted

From: Zi Yan <ziy@nvidia.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.

This will currently never happen, due to the way we always isolate
MAX_ORDER -1 ranges, correct?

You are right.

quoted

Better note that in the patch description, because currently it reads
like it's an actual fix "can be encountered".

Will do. This is a preparation patch for the upcoming commits.

I will drop this one too. Like you mentioned in [1], there are no
non-lru migratable compound pages. This is only used by my local
test code.

[1] https://lore.kernel.org/linux-mm/970ca2a4-416d-7e8f-37c7-510c5b050f4b@redhat.com/ (local)

quoted

quoted

Signed-off-by: Zi Yan <ziy@nvidia.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;

-- 
Thanks,

David / dhildenb

--
Best Regards,
Yan, Zi

--
Best Regards,
Yan, Zi