f2fs: add recovery routines for roll-forward
This adds roll-forward routines to recover fsynced data.
- F2FS uses basically roll-back model with checkpointing.
- In order to implement fsync(), there are two approaches as follows.
1. A roll-back model with checkpointing at every fsync()
: This is a naive method, but suffers from very low performance.
2. A roll-forward model
: F2FS adopts this model where all the fsynced data should be recovered, which
were written after checkpointing was done. In order to figure out the data,
F2FS keeps a "fsync" mark in direct node blocks. In addition, F2FS remains
the location of next node block in each direct node block for reconstructing
the chain of node blocks during the recovery.
- In order to enhance the performance, F2FS keeps a "dentry" mark also in direct
node blocks. If this is set during the recovery, F2FS replays adding a dentry.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
1 file changed