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. Would that work? -- Jeff Layton <jlayton@xxxxxxxxxx>
