Messages in this thread | | | From | Yosry Ahmed <> | Date | Mon, 14 Aug 2023 17:50:46 -0700 | Subject | Re: [PATCH] mm: memcg: provide accurate stats for userspace reads |
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On Mon, Aug 14, 2023 at 5:48 PM Tejun Heo <tj@kernel.org> 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
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