Messages in this thread | | | Date | Tue, 23 Aug 2022 11:42:27 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH 1/3] mm: page_counter: remove unneeded atomic ops for low/min |
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On Mon 22-08-22 17:20:02, Michal Hocko wrote: > On Mon 22-08-22 07:55:58, Shakeel Butt wrote: > > On Mon, Aug 22, 2022 at 3:18 AM Michal Hocko <mhocko@suse.com> wrote: [...] > > > Unless I have missed anything this shouldn't break the correctness but I > > > still have to think about the proportional distribution of the > > > protection because that adds to the complexity here. > > > > The patch is not changing any semantics. It is just removing an > > unnecessary atomic xchg() for a specific scenario (min > 0 && min < > > usage). I don't think there will be any change related to proportional > > distribution of the protection. > > Yes, I suspect you are right. I just remembered previous fixes > like 503970e42325 ("mm: memcontrol: fix memory.low proportional > distribution") which just made me nervous that this is a tricky area. > > I will have another look tomorrow with a fresh brain and send an ack.
I cannot spot any problem. But I guess it would be good to have a little comment to explain that races on the min_usage update (mentioned by Roman) are acceptable and savings from atomic update are preferred.
The worst case I can imagine would be something like uncharge 4kB racing with charge 2MB. The first reduces the protection (min_usage) while the other one misses that update and doesn't increase it. But even then the effect shouldn't be really large. At least I have hard time imagine this would throw things off too much. -- Michal Hocko SUSE Labs
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