Hi Andreas, On Thu, 30 Jan 2014 03:46:59 +0100, Andreas Rohner wrote: > Hi, > > This is only a hacky proof of concept implementation and probably > full of nasty bugs. I also havn't really tested it. I was > just interested how hard it would be to implement Clemens' suggestion > of writing the super block only at umount time and do a linear scan > of all the segments in case of file system failure. > The linear scan is only performed if the file system wasn't shut down > properly. So for normal operation there shouldn't be any slowdown. This premise is not acceptable. We have to avoid long mount time even after unexpected power failures. I prefer some sort of way which combines binary search of segment summary blocks and partial linear scan of logs. I don't know the latency of recent SSDs, however we should estimate the latency of disk I/O about 5ms~20ms per a separate block (in the case of hard drives). So the maximum number of scans of segment summary blocks seems to be roughly 10~100 times. Regards, Ryusuke Konishi > > I repurposed the ss_pad field of nilfs_segment_summary to contain the > crc seed, because I needed a way to distinguish left over segments > from previous nilfs2 volumes from real segments that are part of the > current file system. > > I don't really expect it to be merged or anything. Maybe it can spark > a discussion. Maybe somebody could try it out on an old SD-Card and > time the mount command or something. > > I tested it on a virtual machine. It seemed to recover fine when I > killed the VM and mounted it again. Clearly more testing is > necessary... > > br, > Andreas Rohner > > --- > Andreas Rohner (1): > nilfs2: add mount option that reduces super block writes > > fs/nilfs2/segbuf.c | 3 ++- > fs/nilfs2/segment.c | 3 ++- > fs/nilfs2/super.c | 10 +++++++-- > fs/nilfs2/the_nilfs.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--- > include/linux/nilfs2_fs.h | 4 +++- > 5 files changed, 66 insertions(+), 8 deletions(-) > > -- > 1.8.5.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
