f2fs-for-5.13-rc1 In this round, we added a new mount option, "checkpoint_merge", which introduces a kernel thread dealing with the f2fs checkpoints. Once we start to manage the IO priority along with blk-cgroup, the checkpoint operation can be processed in a lower priority under the process context. Since the checkpoint holds all the filesystem operations, we give a higher priority to the checkpoint thread all the time. Enhancement: - introduce gc_merge mount option to introduce a checkpoint thread - improve to run discard thread efficiently - allow modular compression algorithms - expose # of overprivision segments to sysfs - expose runtime compression stat to sysfs Bug fix: - fix OOB memory access by the node id lookup - avoid touching checkpointed data in the checkpoint-disabled mode - fix the resizing flow to avoid kernel panic and race conditions - fix block allocation issues on pinned files - address some swapfile issues - fix hugtask problem and kernel panic during atomic write operations - don't start checkpoint thread in RO And, we've cleaned up some kernel coding style and build warnings. In addition, we fixed some minor race conditions and error handling routines.