On 2023/3/23 5:34, Andreas Dilger wrote: > On Mar 21, 2023, at 7:33 PM, Zhang Yi <yi.zhang@xxxxxxxxxxxxxxx> wrote: >> This patch set add a new journal option 'JBD2_CYCLE_RECORD' and always >> enable on ext4. It saves journal head for a clean unmounted file system >> in the journal super block, which could let us record journal >> transactions between each mount continuously. It could help us to do >> journal backtrack and find root cause from a corrupted filesystem. >> Current filesystem's corruption analysis is difficult and less useful >> information, especially on the real products. It is useful to some >> extent, especially for the cases of doing fuzzy tests and deploy in some >> shout-runing products. > > Another interesting side benefit of this change is that it gets a step > closer to the "lazy ext4" (log-structured optimization) that had been > described some time ago at FAST: > > https://lwn.net/Articles/720226/ > https://www.usenix.org/system/files/conference/fast17/fast17-aghayev.pdf > https://lists.openwall.net/linux-ext4/2017/04/11/1 > > Essentially, free space in the filesystem (or a large external device) > could be used as a continuous journal, and metadata would only rarely > be checkpointed to the actual filesystem. If the "journal" is close to > wrapping to the start, either the meta/data is checkpointed (if it is > no longer actively used or can make a large write), or re-journaled to > the end of the journal. At remount time, the full journal is read into > memory (discarding old copies of blocks) and this is used to identify > the current metadata rather than reading from the filesystem itself. > > This would allow e.g. very efficient flash caching of metadata (and also > journaled data for small writes) for an HDD (or QLC) device. > This is interesting, but current change looks like is just one small step. It's been almost 6 years after the last talk I can found[1]. Is there anyone still working on it? [1] https://lore.kernel.org/linux-ext4/6B0F0C59-6930-41B3-8EE4-EA5BEECEB9F9@xxxxxxxxx/ Thanks, Yi.
