ext4: add a new helper to check if es must be kept

In the extent status tree, we have extents which we can just drop without
issues and extents we must not drop - this depends on the extent's status
- currently ext4_es_is_delayed() extents must stay, others may be dropped.

A helper function is added to help determine if the current extent can
be dropped, although only ext4_es_is_delayed() extents cannot be dropped
currently.
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230424033846.4732-3-libaokun1@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents_status.c

@@ -446,6 +446,19 @@ static void ext4_es_list_del(struct inode *inode)
 	spin_unlock(&sbi->s_es_lock);
 }
 
+/*
+ * Returns true if we cannot fail to allocate memory for this extent_status
+ * entry and cannot reclaim it until its status changes.
+ */
+static inline bool ext4_es_must_keep(struct extent_status *es)
+{
+	/* fiemap, bigalloc, and seek_data/hole need to use it. */
+	if (ext4_es_is_delayed(es))
+		return true;
+
+	return false;
+}
+
 static struct extent_status *
 ext4_es_alloc_extent(struct inode *inode, ext4_lblk_t lblk, ext4_lblk_t len,
 		     ext4_fsblk_t pblk)
@@ -458,10 +471,8 @@ ext4_es_alloc_extent(struct inode *inode, ext4_lblk_t lblk, ext4_lblk_t len,
 	es->es_len = len;
 	es->es_pblk = pblk;
 
-	/*
-	 * We don't count delayed extent because we never try to reclaim them
-	 */
-	if (!ext4_es_is_delayed(es)) {
+	/* We never try to reclaim a must kept extent, so we don't count it. */
+	if (!ext4_es_must_keep(es)) {
 		if (!EXT4_I(inode)->i_es_shk_nr++)
 			ext4_es_list_add(inode);
 		percpu_counter_inc(&EXT4_SB(inode->i_sb)->
@@ -479,8 +490,8 @@ static void ext4_es_free_extent(struct inode *inode, struct extent_status *es)
 	EXT4_I(inode)->i_es_all_nr--;
 	percpu_counter_dec(&EXT4_SB(inode->i_sb)->s_es_stats.es_stats_all_cnt);
 
-	/* Decrease the shrink counter when this es is not delayed */
-	if (!ext4_es_is_delayed(es)) {
+	/* Decrease the shrink counter when we can reclaim the extent. */
+	if (!ext4_es_must_keep(es)) {
 		BUG_ON(EXT4_I(inode)->i_es_shk_nr == 0);
 		if (!--EXT4_I(inode)->i_es_shk_nr)
 			ext4_es_list_del(inode);
@@ -851,7 +862,7 @@ int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 	if (err == -ENOMEM && __es_shrink(EXT4_SB(inode->i_sb),
 					  128, EXT4_I(inode)))
 		goto retry;
-	if (err == -ENOMEM && !ext4_es_is_delayed(&newes))
+	if (err == -ENOMEM && !ext4_es_must_keep(&newes))
 		err = 0;
 
 	if (sbi->s_cluster_ratio > 1 && test_opt(inode->i_sb, DELALLOC) &&
@@ -1702,11 +1713,8 @@ static int es_do_reclaim_extents(struct ext4_inode_info *ei, ext4_lblk_t end,
 
 		(*nr_to_scan)--;
 		node = rb_next(&es->rb_node);
-		/*
-		 * We can't reclaim delayed extent from status tree because
-		 * fiemap, bigallic, and seek_data/hole need to use it.
-		 */
-		if (ext4_es_is_delayed(es))
+
+		if (ext4_es_must_keep(es))
 			goto next;
 		if (ext4_es_is_referenced(es)) {
 			ext4_es_clear_referenced(es);
@@ -1770,7 +1778,7 @@ void ext4_clear_inode_es(struct inode *inode)
 	while (node) {
 		es = rb_entry(node, struct extent_status, rb_node);
 		node = rb_next(node);
-		if (!ext4_es_is_delayed(es)) {
+		if (!ext4_es_must_keep(es)) {
 			rb_erase(&es->rb_node, &tree->root);
 			ext4_es_free_extent(inode, es);
 		}