On Mon, Aug 14, 2023 at 5:48 PM Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, > > On Mon, Aug 14, 2023 at 05:39:15PM -0700, Yosry Ahmed wrote: > > I believe dropping unified flushing, if possible of course, may fix > > both problems. > > Yeah, flushing the whole tree for every stat read will push up the big O > complexity of the operation. It shouldn't be too bad because only what's > updated since the last read will need flushing but if you have a really big > machine with a lot of constantly active cgroups, you're still gonna feel it. > So, yeah, drop that and switch the global lock to mutex and we should all be > good? I hope so, but I am not sure. The unified flushing was added initially to mitigate a thundering herd problem from concurrent in-kernel flushers (e.g. concurrent reclaims), but back then flushing was atomic so we had to keep the spinlock held for a long time. I think it should be better now, but I am hoping Shakeel will chime in since he added the unified flushing originally. We also need to agree on what to do about stats_flushing_threshold and flush_next_time since they're both global now (since all flushing is global). > > Thanks. > > -- > tejun
