linux-kernel - [PATCH 1/4] ext4: make ext4_es_cache_extent() support overwrite existing extents

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Message-ID: <20251031062905.4135909-2-yi.zhang@huaweicloud.com>
Date: Fri, 31 Oct 2025 14:29:02 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	libaokun1@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH 1/4] ext4: make ext4_es_cache_extent() support overwrite existing extents

From: Zhang Yi <yi.zhang@...wei.com>

Currently, ext4_es_cache_extent() is used to load extents into the
extent status tree when reading on-disk extent blocks. Since it may be
called while moving or modifying the extent tree, so it does not
overwrite existing extents in the extent status tree and is only used
for the initial loading.

There are many other places in ext4 where on-disk extents are inserted
into the extent status tree, such as in ext4_map_query_blocks().
Currently, they call ext4_es_insert_extent() to perform the insertion,
but they don't modify the extents, so ext4_es_cache_extent() would be a
more appropriate choice. However, when ext4_map_query_blocks() inserts
an extent, it may overwrite a short existing extent of the same type.
Therefore, to prepare for the replacements, we need to extend
ext4_es_cache_extent() to allow it to overwrite existing extents with
the same type.

In addition, since cached extents can be more lenient than the extents
they modify and do not involve modifying reserved blocks, it is not
necessary to ensure that the insertion operation succeeds as strictly as
in the ext4_es_insert_extent() function.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
 fs/ext4/extents.c        |  4 ++--
 fs/ext4/extents_status.c | 28 +++++++++++++++++++++-------
 fs/ext4/extents_status.h |  2 +-
 3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ca5499e9412b..c42ceb5aae37 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -537,12 +537,12 @@ static void ext4_cache_extents(struct inode *inode,
 
 		if (prev && (prev != lblk))
 			ext4_es_cache_extent(inode, prev, lblk - prev, ~0,
-					     EXTENT_STATUS_HOLE);
+					     EXTENT_STATUS_HOLE, false);
 
 		if (ext4_ext_is_unwritten(ex))
 			status = EXTENT_STATUS_UNWRITTEN;
 		ext4_es_cache_extent(inode, lblk, len,
-				     ext4_ext_pblock(ex), status);
+				     ext4_ext_pblock(ex), status, false);
 		prev = lblk + len;
 	}
 }
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 31dc0496f8d0..f9546ecf7340 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -986,13 +986,19 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 }
 
 /*
- * ext4_es_cache_extent() inserts information into the extent status
- * tree if and only if there isn't information about the range in
- * question already.
+ * ext4_es_cache_extent() inserts extent information into the extent status
+ * tree. If 'overwrite' is not set, it inserts extent only if there isn't
+ * information about the specified range. Otherwise, it overwrites the
+ * current information.
+ *
+ * Note that this interface is only used for caching on-disk extent
+ * information and cannot be used to convert existing extents in the extent
+ * status tree. To convert existing extents, use ext4_es_insert_extent()
+ * instead.
  */
 void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 			  ext4_lblk_t len, ext4_fsblk_t pblk,
-			  unsigned int status)
+			  unsigned int status, bool overwrite)
 {
 	struct extent_status *es;
 	struct extent_status newes;
@@ -1012,10 +1018,18 @@ void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 	BUG_ON(end < lblk);
 
 	write_lock(&EXT4_I(inode)->i_es_lock);
-
 	es = __es_tree_search(&EXT4_I(inode)->i_es_tree.root, lblk);
-	if (!es || es->es_lblk > end)
-		__es_insert_extent(inode, &newes, NULL);
+	if (es && es->es_lblk <= end) {
+		if (!overwrite)
+			goto unlock;
+
+		/* Only extents of the same type can be overwritten. */
+		WARN_ON_ONCE(ext4_es_type(es) != status);
+		if (__es_remove_extent(inode, lblk, end, NULL, NULL))
+			goto unlock;
+	}
+	__es_insert_extent(inode, &newes, NULL);
+unlock:
 	write_unlock(&EXT4_I(inode)->i_es_lock);
 }
 
diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
index 8f9c008d11e8..415f7c223a46 100644
--- a/fs/ext4/extents_status.h
+++ b/fs/ext4/extents_status.h
@@ -139,7 +139,7 @@ extern void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 				  bool delalloc_reserve_used);
 extern void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 				 ext4_lblk_t len, ext4_fsblk_t pblk,
-				 unsigned int status);
+				 unsigned int status, bool overwrite);
 extern void ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 				  ext4_lblk_t len);
 extern void ext4_es_find_extent_range(struct inode *inode,
-- 
2.46.1