On Thu 22-09-22 16:18:02, Jeff Layton wrote: > On Thu, 2022-09-22 at 06:18 -0400, Jeff Layton wrote: > > On Thu, 2022-09-22 at 07:41 +1000, Dave Chinner wrote: > > > e.g. The NFS server can track the i_version values when the NFSD > > > syncs/commits a given inode. The nfsd can sample i_version it when > > > calls ->commit_metadata or flushed data on the inode, and then when > > > it peeks at i_version when gathering post-op attrs (or any other > > > getattr op) it can decide that there is too much in-memory change > > > (e.g. 10,000 counts since last sync) and sync the inode. > > > > > > i.e. the NFS server can trivially cap the maximum number of > > > uncommitted NFS change attr bumps it allows to build up in memory. > > > At that point, the NFS server has a bound "maximum write count" that > > > can be used in conjunction with the xattr based crash counter to > > > determine how the change_attr is bumped by the crash counter. > > > > Well, not "trivially". This is the bit where we have to grow struct > > inode (or the fs-specific inode), as we'll need to know what the latest > > on-disk value is for the inode. > > > > I'm leaning toward doing this on the query side. Basically, when nfsd > > goes to query the i_version, it'll check the delta between the current > > version and the latest one on disk. If it's bigger than X then we'd just > > return NFS4ERR_DELAY to the client. > > > > If the delta is >X/2, maybe it can kick off a workqueue job or something > > that calls write_inode with WB_SYNC_ALL to try to get the thing onto the > > platter ASAP. > > Still looking at this bit too. Probably we can just kick off a > WB_SYNC_NONE filemap_fdatawrite at that point and hope for the best? "Hope" is not a great assurance regarding data integrity ;) Anyway, it depends on how you imagine the "i_version on disk" is going to be maintained. It could be maintained by NFSD inside commit_inode_metadata() - fetch current i_version value before asking filesystem for the sync and by the time commit_metadata() returns we know that value is on disk. If we detect the current - on_disk is > X/2, we call commit_inode_metadata() and we are done. It is not even *that* expensive because usually filesystems optimize away unnecessary IO when the inode didn't change since last time it got synced. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
