On Mon, Aug 14, 2023 at 5:30 PM Ivan Babrou <ivan@xxxxxxxxxxxxxx> wrote: > > On Mon, Aug 14, 2023 at 5:18 PM Tejun Heo <tj@xxxxxxxxxx> wrote: > > > > Hello, > > > > On Fri, Aug 11, 2023 at 05:01:08PM -0700, Yosry Ahmed wrote: > > > There have been a lot of problems coming from this global rstat lock: > > > hard lockups (when we used to flush atomically), unified flushing > > > being expensive, skipping flushing being inaccurate, etc. > > > > > > I wonder if it's time to rethink this lock and break it down into > > > granular locks. Perhaps a per-cgroup lock, and develop a locking > > > scheme where you always lock a parent then a child, then flush the > > > child and unlock it and move to the next child, etc. This will allow > > > concurrent flushing of non-root cgroups. Even when flushing the root, > > > if we flush all its children first without locking the root, then only > > > lock the root when flushing the top-level children, then some level of > > > concurrency can be achieved. > > > > > > Maybe this is too complicated, I never tried to implement it, but I > > > have been bouncing around this idea in my head for a while now. > > > > > > We can also split the update tree per controller. As far as I can tell > > > there is no reason to flush cpu stats for example when someone wants > > > to read memory stats. > > > > There's another thread. Let's continue there but I'm a bit skeptical whether > > splitting the lock is a good solution here. Regardless of locking, we don't > > want to run in an atomic context for that long anwyay. > > Could you link to the other thread? I supposedly CC'd you there, but I realized it didn't work for some reason: https://lore.kernel.org/lkml/CAJD7tkYBFz-gZ2QsHxUMT=t0KNXs66S-zzMPebadHx9zaG0Q3w@xxxxxxxxxxxxxx/
