On Tue, 2017-06-06 at 09:00 -0400, Benjamin Coddington wrote: > > On 5 Jun 2017, at 18:02, Jeff Layton wrote: > > > On Mon, 2017-06-05 at 14:34 -0400, Benjamin Coddington wrote: > > > On 1 Jun 2017, at 11:48, Jeff Layton wrote: > > > > > > > On Thu, 2017-06-01 at 11:14 -0400, J. Bruce Fields wrote: > > > > > On Thu, Jun 01, 2017 at 08:59:21AM -0400, Jeff Layton wrote: > > > > > > I'm not so sure. That would only be the case if the thing were > > > > > > marked > > > > > > for manadatory locking (a really rare thing). > > > > > > > > > > > > The test is really simple and I don't think any read/write > > > > > > activity > > > > > > is > > > > > > involved: > > > > > > > > > > > > https://github.com/antonblanchard/will-it-scale/blob/master/tests/lock1.c > > > > > > > > > > So it's just F_WRLCK/F_UNLCK in a loop spread across multiple > > > > > cores? > > > > > I'd think real workloads do some work while holding the lock, and a > > > > > 15% > > > > > regression on just the pure lock/unlock loop might not matter? But > > > > > best > > > > > to be careful, I guess. > > > > > > > > > > --b. > > > > > > > > > > > > > Yeah, that's my take. > > > > > > > > I was assuming that getting a pid reference would be essentially > > > > free, > > > > but it doesn't seem to be. > > > > > > > > So, I think we probably want to avoid taking it for a file_lock that > > > > we > > > > use to request a lock, but do take it for a file_lock that is used > > > > to > > > > record a lock. How best to code that up, I'm not quite sure... > > > > > > Maybe as simple as only setting fl_nspid in locks_insert_lock_ctx(), > > > but > > > that seems to just take us back to the problem of getting the pid > > > wrong > > > if > > > the lock is inserted later by a different worker than created the > > > request. > > > > > > I have a mind now to just drop fl_nspid off the struct file_lock > > > completely, > > > and instead just carry fl_pid, and when we do F_GETLK, we can do: > > > > > > task = find_task_by_pid_ns(fl_pid, init_pid_ns) > > > fl_nspid = task_pid_nr_ns(task, task_active_pid_ns(current)) > > > > > > That moves all the work off into the F_GETLK case, which I think is > > > not > > > used > > > so much. > > > > > > > Actually I think what might work best is to: > > > > - have locks_copy_conflock also copy the fl_nspid and take a reference > > to it (as your patch #2 does) > > > > - only set fl_nspid and take a reference there in > > locks_insert_lock_ctx > > if it's not already set > > > > - allow ->lock operations (like nfs) to set fl_nspid before they call > > locks_lock_inode_wait to set the local lock. Might need to take a > > nspid > > reference before dispatching an RPC so that you get the right thread > > context. > > It would, but I think fl_nspid is completely unnecessary. The reason we > have it so that we can translate the pid number into other namespaces, > the > most common case being that F_GETLK and views of /proc/locks within a > namespace represent the same pid numbers as the processes in that > namespace > that are holding the locks. > > It is much simpler to just keep using fl_pid as the pid number in the > init > namespace, but move the translation of that pid number to lookup time, > rather than creation time. > I think that would also work and I like the idea of getting rid of a field in file_lock. So, to be clear: fl_pid would then store the pid of the process in the init_pid_ns, and you'd just translate it as appropriate to the requestor's namespace? If we want to go that route, then you'll probably still need a flag of some sort to indicate that the fl_pid is to be expressed "as is", for remote filesystems. OTOH, if the lock is held remotely, I wonder if we'd be better off simply reporting the pid as '-1', like we do with OFD locks. Hardly anything pays attention to l_pid anyway and it's more or less meaningless once the filesystem extends beyond the machine you're on. That said, I'd be inclined to do that in a separate set so we could revert it if it caused problems somewhere. -- Jeff Layton <jlayton@xxxxxxxxxx>
