From: Zhang Yi <yi.zhang@xxxxxxxxxx> Now ext4 only reserved space for delalloc for data blocks in ext4_da_reserve_space(), not reserve space for meta blocks when allocating data blocks. Besides, if we enable dioread_nolock mount option, it also not reserve meta blocks for the unwritten extents to written extents conversion. In order to prevent data loss due to failed to allocate meta blocks when writing data back, we reserve 2% space or 4096 blocks for meta data, and use EXT4_GET_BLOCKS_PRE_IO to do the potential split in advance. But all these two methods are just best efforts, if it's really running out of sapce, there is no difference between splitting extent when writing data back and when I/Os are completed, both will result in data loss. The best way is to reserve enough space for metadata. Before that, we can at least make sure that things will not get worse if we postpone splitting extent in endio. Plus, after converting regular file's buffered write path from buffer_head to iomap, splitting extents in endio becomes mandatory. Now, in preparation for the future conversion, let's use reserved sapce in endio too. Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx> --- fs/ext4/extents.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index fc69f13cf510..254f8b85653d 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -3722,7 +3722,8 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle, (unsigned long long)map->m_lblk, map->m_len); #endif err = ext4_split_convert_extents(handle, inode, map, ppath, - EXT4_GET_BLOCKS_CONVERT); + EXT4_GET_BLOCKS_CONVERT | + EXT4_GET_BLOCKS_METADATA_NOFAIL); if (err < 0) return err; path = ext4_find_extent(inode, map->m_lblk, ppath, 0); -- 2.39.2
