----- Original Message ----- > From: "John Spray" <john.spray@xxxxxxxxxx> > To: ceph-devel@xxxxxxxxxxxxxxx, zyan@xxxxxxxxxx, "Gregory Farnum" <gfarnum@xxxxxxxxxx> > Sent: Thursday, February 19, 2015 2:23:21 PM > Subject: ceph-fuse remount issues > > > Background: a while ago, we found (#10277) that existing cache > expiration mechanism wasn't working with latest kernels. We used to > invalidate the top level dentries, which caused fuse to invalidate > everything, but an implementation detail in fuse caused it to start > ignoring our repeated invalidate calls, so this doesn't work any more. > To persuade fuse to dirty its entire metadata cache, Zheng added in a > system() call to "mount -o remount" after we expire things from our > client side cache. > > However, this was a bit of a hack and has created problems: > * You can't call mount -o remount unless you're root, so we are less > flexible than we used to be (#10542) > * While the remount is happening, unmounts sporadically fail and the > fuse process can become unresponsive to SIGKILL (#10916) > > The first issue was maybe an acceptable compromise, but the second issue > is just painful, and it seems like we might not have seen the last of > the knock on effects -- upstream maintainers certainly aren't expecting > filesystems to remount themselves quite so frequently. Yeah. I looked at this briefly and switching to a conditional behavior based on kernel version shouldn't be too difficult; the actual change in behavior is a very short patch: https://github.com/ceph/ceph/commit/0827bb79ea5127e6763f6e904dfa1a3266046ffb I'm going to try and integrate that in with my branch to warn on remount issues in the morning: https://github.com/ceph/ceph/pull/3681 (better version of that sitting on my computer now too) > We probably have an opportunity to get something upstream in fuse to > support a direct call to trigger the invalidation we want, if we can > work out what that should look like. Thoughts? Yes please. I don't really have the kernel VFS or FUSE interface experience here to offer up much off the top of my head, but I think this is something that FUSE ought to allow us to do. LSF/MM is coming up and Sage will be there, which is probably a good time to raise issues with people in the hallway or appropriate sessions. -Greg -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
