On Mon, 2023-10-23 at 14:18 -1000, Linus Torvalds wrote: > On Mon, 23 Oct 2023 at 13:26, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > The problem is the first read request after a modification has been > > made. That is causing relatime to see mtime > atime and triggering > > an atime update. XFS sees this, does an atime update, and in > > committing that persistent inode metadata update, it calls > > inode_maybe_inc_iversion(force = false) to check if an iversion > > update is necessary. The VFS sees I_VERSION_QUERIED, and so it bumps > > i_version and tells XFS to persist it. > > Could we perhaps just have a mode where we don't increment i_version > for just atime updates? > > Maybe we don't even need a mode, and could just decide that atime > updates aren't i_version updates at all? > > Yes, yes, it's obviously technically a "inode modification", but does > anybody actually *want* atime updates with no actual other changes to > be version events? > > Or maybe i_version can update, but callers of getattr() could have two > bits for that STATX_CHANGE_COOKIE, one for "I care about atime" and > one for others, and we'd pass that down to inode_query_version, and > we'd have a I_VERSION_QUERIED and a I_VERSION_QUERIED_STRICT, and the > "I care about atime" case ould set the strict one. > > Then inode_maybe_inc_iversion() could - for atome updates - skip the > version update *unless* it sees that I_VERSION_QUERIED_STRICT bit. > > Does that sound sane to people? > > Because it does sound completely insane to me to say "inode changed" > and have a cache invalidation just for an atime update. > The new flag idea is a good one. The catch though is that there are no readers of i_version in-kernel other than NFSD and IMA, so there would be no in-kernel users of I_VERSION_QUERIED_STRICT. In earlier discussions, I was given to believe that the problem with changing how this works in XFS involved offline filesystem access tools. That said, I didn't press for enough details at the time, so I may have misunderstood Dave's reticence to change how this works. -- Jeff Layton <jlayton@xxxxxxxxxx>
