On Mon, Feb 27, 2023 at 06:45:50PM +0800, Gao Xiang wrote: > > (+cc Jingbo Xu and Christian Brauner) > > On 2023/2/27 17:22, Alexander Larsson wrote: > > Hello, > > > > Recently Giuseppe Scrivano and I have worked on[1] and proposed[2] the > > Composefs filesystem. It is an opportunistically sharing, validating > > image-based filesystem, targeting usecases like validated ostree > > rootfs:es, validated container images that share common files, as well > > as other image based usecases. > > > > During the discussions in the composefs proposal (as seen on LWN[3]) > > is has been proposed that (with some changes to overlayfs), similar > > behaviour can be achieved by combining the overlayfs > > "overlay.redirect" xattr with an read-only filesystem such as erofs. > > > > There are pros and cons to both these approaches, and the discussion > > about their respective value has sometimes been heated. We would like > > to have an in-person discussion at the summit, ideally also involving > > more of the filesystem development community, so that we can reach > > some consensus on what is the best apporach. > > > > Good participants would be at least: Alexander Larsson, Giuseppe > > Scrivano, Amir Goldstein, David Chinner, Gao Xiang, Miklos Szeredi, > > Jingbo Xu > I'd be happy to discuss this at LSF/MM/BPF this year. Also we've addressed > the root cause of the performance gap is that > > composefs read some data symlink-like payload data by using > cfs_read_vdata_path() which involves kernel_read() and trigger heuristic > readahead of dir data (which is also landed in composefs vdata area > together with payload), so that most composefs dir I/O is already done > in advance by heuristic readahead. And we think almost all exist > in-kernel local fses doesn't have such heuristic readahead and if we add > the similar stuff, EROFS could do better than composefs. > > Also we've tried random stat()s about 500~1000 files in the tree you shared > (rather than just "ls -lR") and EROFS did almost the same or better than > composefs. I guess further analysis (including blktrace) could be shown by > Jingbo later. > > Not sure if Christian Brauner would like to discuss this new stacked fs I'll be at lsfmm in any case and already got my invite a while ago. I intend to give some updates about a few vfs things and I can talk about this as well. Thanks, Gao!
