Hi, i see massive data rewrites of defragmented files when work with btrfs fi def <args>. Before, i just thought it's a design problem - i.e. defrag always rewrite data to new place.
At now, i read the code and see 2 bad cases: 1. With -c<compression_algo> all extents of data will be rewriten, always. 2. btrfs use "bad" default target extent size, i.e. kernel by default try get 256KiB extent, btrfs-progres use 32MiB as a threshold. Both of them make ioctl code should_defrag_range() think, that extent are "too" fragmented, and rewrite all compressed extents. Does that behavior expected? i.e. only way that i can safely use on my data are: btrfs fi def -vr -t 128KiB <path> That will defrag all fragmented compressed extents. "Hacky" solution that i see for now, is a create copy of inode_need_compress() for defrag ioctl, and if file must be compressed, force use of 128KiB as target extent. or at least document that not obvious behaviour. Thanks! -- Have a nice day, Timofey. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
