[PATCH RFC 03/13] mm/huge_memory: invert folio_ref_freeze() check to reduce indentation

[Kairui Song via B4 Relay]

From: Kairui Song <kasong@xxxxxxxxxxx>

Invert the folio_ref_freeze() success check in
__folio_freeze_and_split_unmapped() to return early on failure, which
removes one level of indentation from the entire success path.

This is a pure refactoring with no functional change.  It prepares the
function to be split into separate helpers for anonymous and
file-backed folios in a later patch.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/huge_memory.c | 181 +++++++++++++++++++++++++++----------------------------
 1 file changed, 90 insertions(+), 91 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2fa72158e063..cf8f90b94e42 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3941,9 +3941,11 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 					     pgoff_t end, int *nr_shmem_dropped)
 {
 	struct folio *end_folio = folio_next(folio);
+	struct swap_cluster_info *ci = NULL;
 	struct folio *new_folio, *next;
 	int old_order = folio_order(folio);
 	struct list_lru_one *lru;
+	struct lruvec *lruvec;
 	bool dequeue_deferred;
 	int ret = 0;
 
@@ -3964,122 +3966,119 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
 		lru = list_lru_lock(&deferred_split_lru,
 				    folio_nid(folio), &memcg);
 	}
-	if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
-		struct swap_cluster_info *ci = NULL;
-		struct lruvec *lruvec;
 
+	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
 		if (dequeue_deferred) {
-			__list_lru_del(&deferred_split_lru, lru,
-				       &folio->_deferred_list, folio_nid(folio));
-			if (folio_test_partially_mapped(folio)) {
-				folio_clear_partially_mapped(folio);
-				mod_mthp_stat(old_order,
-					MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
-			}
 			list_lru_unlock(lru);
 			rcu_read_unlock();
 		}
+		return -EAGAIN;
+	}
 
-		if (mapping) {
-			int nr = folio_nr_pages(folio);
-
-			if (folio_test_pmd_mappable(folio) &&
-			    new_order < HPAGE_PMD_ORDER) {
-				if (folio_test_swapbacked(folio)) {
-					lruvec_stat_mod_folio(folio,
-							NR_SHMEM_THPS, -nr);
-				} else {
-					lruvec_stat_mod_folio(folio,
-							NR_FILE_THPS, -nr);
-				}
-			}
+	if (dequeue_deferred) {
+		__list_lru_del(&deferred_split_lru, lru,
+			       &folio->_deferred_list, folio_nid(folio));
+		if (folio_test_partially_mapped(folio)) {
+			folio_clear_partially_mapped(folio);
+			mod_mthp_stat(old_order,
+				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 		}
+		list_lru_unlock(lru);
+		rcu_read_unlock();
+	}
 
-		if (folio_test_swapcache(folio))
-			ci = swap_cluster_get_and_lock(folio);
-
-		/* lock lru list/PageCompound, ref frozen by page_ref_freeze */
-		if (do_lru)
-			lruvec = folio_lruvec_lock(folio);
-
-		ret = __split_unmapped_folio(folio, new_order, split_at, xas,
-					     mapping, split_type);
+	if (mapping) {
+		int nr = folio_nr_pages(folio);
 
-		/*
-		 * Unfreeze after-split folios and put them back to the right
-		 * list. @folio should be kept frozon until page cache
-		 * entries are updated with all the other after-split folios
-		 * to prevent others seeing stale page cache entries.
-		 * As a result, new_folio starts from the next folio of
-		 * @folio.
-		 */
-		for (new_folio = folio_next(folio); new_folio != end_folio;
-		     new_folio = next) {
-			unsigned long nr_pages = folio_nr_pages(new_folio);
+		if (folio_test_pmd_mappable(folio) &&
+		    new_order < HPAGE_PMD_ORDER) {
+			if (folio_test_swapbacked(folio)) {
+				lruvec_stat_mod_folio(folio,
+						      NR_SHMEM_THPS, -nr);
+			} else {
+				lruvec_stat_mod_folio(folio,
+						      NR_FILE_THPS, -nr);
+			}
+		}
+	}
 
-			next = folio_next(new_folio);
+	if (folio_test_swapcache(folio))
+		ci = swap_cluster_get_and_lock(folio);
 
-			zone_device_private_split_cb(folio, new_folio);
+	/* lock lru list/PageCompound, ref frozen by page_ref_freeze */
+	if (do_lru)
+		lruvec = folio_lruvec_lock(folio);
 
-			folio_ref_unfreeze(new_folio,
-					   folio_cache_ref_count(new_folio) + 1);
+	ret = __split_unmapped_folio(folio, new_order, split_at, xas,
+				     mapping, split_type);
 
-			if (do_lru)
-				lru_add_split_folio(folio, new_folio, lruvec, list);
+	/*
+	 * Unfreeze after-split folios and put them back to the right
+	 * list. @folio should be kept frozon until page cache
+	 * entries are updated with all the other after-split folios
+	 * to prevent others seeing stale page cache entries.
+	 * As a result, new_folio starts from the next folio of
+	 * @folio.
+	 */
+	for (new_folio = folio_next(folio); new_folio != end_folio;
+	     new_folio = next) {
+		unsigned long nr_pages = folio_nr_pages(new_folio);
 
-			/*
-			 * Anonymous folio with swap cache.
-			 * NOTE: shmem in swap cache is not supported yet.
-			 */
-			if (ci) {
-				__swap_cache_replace_folio(ci, folio, new_folio);
-				continue;
-			}
+		next = folio_next(new_folio);
 
-			/* Anonymous folio without swap cache */
-			if (!mapping)
-				continue;
+		zone_device_private_split_cb(folio, new_folio);
 
-			/* Add the new folio to the page cache. */
-			if (new_folio->index < end) {
-				__xa_store(&mapping->i_pages, new_folio->index,
-					   new_folio, 0);
-				continue;
-			}
+		folio_ref_unfreeze(new_folio,
+				   folio_cache_ref_count(new_folio) + 1);
 
-			VM_WARN_ON_ONCE(!nr_shmem_dropped);
-			/* Drop folio beyond EOF: ->index >= end */
-			if (shmem_mapping(mapping) && nr_shmem_dropped)
-				*nr_shmem_dropped += nr_pages;
-			else if (folio_test_clear_dirty(new_folio))
-				folio_account_cleaned(
-					new_folio, inode_to_wb(mapping->host));
-			__filemap_remove_folio(new_folio, NULL);
-			folio_put_refs(new_folio, nr_pages);
-		}
+		if (do_lru)
+			lru_add_split_folio(folio, new_folio, lruvec, list);
 
-		zone_device_private_split_cb(folio, NULL);
 		/*
-		 * Unfreeze @folio only after all page cache entries, which
-		 * used to point to it, have been updated with new folios.
-		 * Otherwise, a parallel folio_try_get() can grab @folio
-		 * and its caller can see stale page cache entries.
+		 * Anonymous folio with swap cache.
+		 * NOTE: shmem in swap cache is not supported yet.
 		 */
-		folio_ref_unfreeze(folio, folio_cache_ref_count(folio) + 1);
+		if (ci) {
+			__swap_cache_replace_folio(ci, folio, new_folio);
+			continue;
+		}
 
-		if (do_lru)
-			lruvec_unlock(lruvec);
+		/* Anonymous folio without swap cache */
+		if (!mapping)
+			continue;
 
-		if (ci)
-			swap_cluster_unlock(ci);
-	} else {
-		if (dequeue_deferred) {
-			list_lru_unlock(lru);
-			rcu_read_unlock();
+		/* Add the new folio to the page cache. */
+		if (new_folio->index < end) {
+			__xa_store(&mapping->i_pages, new_folio->index,
+				   new_folio, 0);
+			continue;
 		}
-		return -EAGAIN;
+
+		VM_WARN_ON_ONCE(!nr_shmem_dropped);
+		/* Drop folio beyond EOF: ->index >= end */
+		if (shmem_mapping(mapping) && nr_shmem_dropped)
+			*nr_shmem_dropped += nr_pages;
+		else if (folio_test_clear_dirty(new_folio))
+			folio_account_cleaned(new_folio,
+					      inode_to_wb(mapping->host));
+		__filemap_remove_folio(new_folio, NULL);
+		folio_put_refs(new_folio, nr_pages);
 	}
 
+	zone_device_private_split_cb(folio, NULL);
+	/*
+	 * Unfreeze @folio only after all page cache entries, which
+	 * used to point to it, have been updated with new folios.
+	 * Otherwise, a parallel folio_try_get() can grab @folio
+	 * and its caller can see stale page cache entries.
+	 */
+	folio_ref_unfreeze(folio, folio_cache_ref_count(folio) + 1);
+
+	if (do_lru)
+		lruvec_unlock(lruvec);
+	if (ci)
+		swap_cluster_unlock(ci);
+
 	return ret;
 }
 

-- 
2.55.0