[RFC PATCH v3 3/4] mm: drain LRU cache if necessary for splitting large folios

["Barry Song (Xiaomi)" <baohua@kernel.org>]

Smaller large folios might now be present in the LRU cache. Use David's
new lru_cache_drain_for_folio() helper to drain the LRU cache before
splitting a folio, ensuring that the folio can be split successfully.

Also, we only perform the drain when it may actually help, assuming
that the lru_cache holds an extra reference.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/huge_memory.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ced400f72d43..263ef9b6949d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4201,6 +4201,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 		if (shmem_mapping(mapping))
 			end = shmem_fallocend(mapping->host, end);
 	}
+	if (folio_ref_count(folio) == folio_expected_ref_count(folio) + 1 +
+	    folio_may_be_lru_cached(folio))
+		lru_cache_drain_for_folio(folio, 1, NULL);
 
 	/*
 	 * Racy check if we can split the page, before unmap_folio() will
@@ -4325,6 +4328,9 @@ int folio_split_unmapped(struct folio *folio, unsigned int new_order)
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio);
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_anon(folio), folio);
 
+	if (folio_ref_count(folio) == folio_expected_ref_count(folio) + 1 +
+	    folio_may_be_lru_cached(folio))
+		lru_cache_drain_for_folio(folio, 1, NULL);
 	if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1)
 		return -EAGAIN;
 
@@ -4805,6 +4811,10 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 			goto next;
 
 		total++;
+
+		if (folio_ref_count(folio) == folio_expected_ref_count(folio) +
+		    folio_may_be_lru_cached(folio))
+			lru_cache_drain_for_folio(folio, 0, NULL);
 		/*
 		 * For folios with private, split_huge_page_to_list_to_order()
 		 * will try to drop it before split and then check if the folio
-- 
2.34.1