On Thu, Dec 11, 2025 at 07:51:42PM +0800, Li Chen wrote:
> Fast commits only log operations that have dedicated replay support.
> EXT4_IOC_GROUP_EXTEND grows the filesystem to the end of the last
> block group and updates the same on-disk metadata without going
> through the fast commit tracking paths.
> In practice these operations are rare and usually followed by further
> updates, but mixing them into a fast commit makes the overall
> semantics harder to reason about and risks replay gaps if new call
> sites appear.
>
> Teach ext4 to mark the filesystem fast-commit ineligible when
> EXT4_IOC_GROUP_EXTEND grows the filesystem.
> This forces those transactions to fall back to a full commit,
> ensuring that the group extension changes are captured by the normal
> journal rather than partially encoded in fast commit TLVs.
> This change should not affect common workloads but makes online
> resize via GROUP_EXTEND safer and easier to reason about under fast
> commit.
>
> Testing:
> 1. prepare:
> dd if=/dev/zero of=/root/fc_resize.img bs=1M count=0 seek=256
> mkfs.ext4 -O fast_commit -F /root/fc_resize.img
> mkdir -p /mnt/fc_resize && mount -t ext4 -o loop /root/fc_resize.img
> /mnt/fc_resize
> 2. Extended the filesystem to the end of the last block group using a
> helper that calls EXT4_IOC_GROUP_EXTEND on the mounted filesystem
> and checked fc_info:
> ./group_extend_helper /mnt/fc_resize
> cat /proc/fs/ext4/loop0/fc_info
> shows the "Resize" ineligible reason increased.
> 3. Fsynced a file on the resized filesystem and confirmed that the fast
> commit ineligible counter incremented for the resize transaction:
> touch /mnt/fc_resize/file
> /root/fsync_file /mnt/fc_resize/file
> sync
> cat /proc/fs/ext4/loop0/fc_info
>
> Signed-off-by: Li Chen <[email protected]>
I'm curious what version of the kernel you were testing against? I
needed to mnake the final fix up to allow the patch to compile:
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 9354083222b1..ce1f738dff93 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -321,7 +321,8 @@ static int mext_move_extent(struct mext_data *mext, u64
*m_len)
ret = PTR_ERR(handle);
goto out;
}
- ext4_fc_mark_ineligible(sb, EXT4_FC_REASON_MOVE_EXT, handle);
+ ext4_fc_mark_ineligible(orig_inode->i_sb, EXT4_FC_REASON_MOVE_EXT,
+ handle);
ret = mext_move_begin(mext, folio, &move_type);
if (ret)
- Ted
