[PATCH v4 08/17] mm/huge_memory: move unmap and remap into the split helpers

[Kairui Song via B4 Relay]

From: Kairui Song <kasong@xxxxxxxxxxx>

To prepare for further cleanup, move the unmap/remap handling from
__folio_split() into the split helpers.  Only anon folios need to
be remapped, so remap_page() is now only called for anon splits and
the anon check in remap_page() is redundant and can be removed.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
Reviewed-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/huge_memory.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 47ccf2326cfe..7d7ce0726c19 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3640,9 +3640,6 @@ static void remap_page(struct folio *folio, unsigned long nr, int flags)
 {
 	int i = 0;
 
-	/* If unmap_folio() uses try_to_migrate() on file, remove this check */
-	if (!folio_test_anon(folio))
-		return;
 	for (;;) {
 		remove_migration_ptes(folio, folio, TTU_RMAP_LOCKED | flags);
 		i += folio_nr_pages(folio);
@@ -3995,14 +3992,21 @@ static int __folio_freeze_split_anon(struct folio *folio,
 	struct swap_cluster_info *ci = NULL;
 	struct folio *new_folio, *next;
 	int old_order = folio_order(folio);
+	enum ttu_flags ttu_flags = 0;
 	struct lruvec *lruvec;
+	bool need_remap = false;
 	int ret = 0;
 
+	if (folio_mapped(folio)) {
+		need_remap = true;
+		unmap_folio(folio);
+	}
+
 	local_irq_disable();
 
 	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
-		local_irq_enable();
-		return -EAGAIN;
+		ret = -EAGAIN;
+		goto out_no_split;
 	}
 
 	/* Take off the deferred split queue while frozen and memcg set */
@@ -4055,7 +4059,13 @@ static int __folio_freeze_split_anon(struct folio *folio,
 		lruvec_unlock(lruvec);
 	if (ci)
 		swap_cluster_unlock(ci);
+out_no_split:
 	local_irq_enable();
+	if (need_remap) {
+		if (!ret && !folio_is_device_private(folio))
+			ttu_flags = TTU_USE_SHARED_ZEROPAGE;
+		remap_page(folio, 1 << old_order, ttu_flags);
+	}
 
 	return ret;
 }
@@ -4087,6 +4097,8 @@ static int __folio_freeze_split_file(struct folio *folio,
 	if (shmem_mapping(mapping))
 		end = shmem_fallocend(mapping->host, end);
 
+	unmap_folio(folio);
+
 	xas_lock_irq(xas);
 
 	/*
@@ -4171,8 +4183,11 @@ static int __folio_freeze_split_file(struct folio *folio,
 
 	if (do_lru)
 		lruvec_unlock(lruvec);
-
 fail:
+	/*
+	 * If we want to use try_to_migrate() on file in unmap_folio,
+	 * remember to add remap_page() and adapt it.
+	 */
 	xas_unlock_irq(xas);
 	if (nr_shmem_dropped)
 		shmem_uncharge(mapping->host, nr_shmem_dropped);
@@ -4212,7 +4227,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 	struct anon_vma *anon_vma = NULL;
 	int old_order = folio_order(folio);
 	struct folio *new_folio, *next;
-	enum ttu_flags ttu_flags = 0;
 	int ret;
 
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
@@ -4300,8 +4314,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 		goto out_unlock;
 	}
 
-	unmap_folio(folio);
-
 	if (is_anon)
 		ret = __folio_freeze_split_anon(folio, new_order, split_at,
 						true, list, split_type);
@@ -4309,11 +4321,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 		ret = __folio_freeze_split_file(folio, new_order, split_at, &xas, mapping,
 						true, list, split_type);
 
-	if (!ret && is_anon && !folio_is_device_private(folio))
-		ttu_flags = TTU_USE_SHARED_ZEROPAGE;
-
-	remap_page(folio, 1 << old_order, ttu_flags);
-
 	/*
 	 * Drop the mapping while the inode is still pinned. @folio stays
 	 * locked and present in the page cache until the loop below, so

-- 
2.55.0