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SubjectRe: [PATCH 6/8] lazy tlb: shoot lazies, a non-refcounting lazy tlb option

> On Dec 2, 2020, at 6:20 AM, Peter Zijlstra <> wrote:
> On Sun, Nov 29, 2020 at 02:01:39AM +1000, Nicholas Piggin wrote:
>> + * - A delayed freeing and RCU-like quiescing sequence based on
>> + * mm switching to avoid IPIs completely.
> That one's interesting too. so basically you want to count switch_mm()
> invocations on each CPU. Then, periodically snapshot the counter on each
> CPU, and when they've all changed, increment a global counter.
> Then, you snapshot the global counter and wait for it to increment
> (twice I think, the first increment might already be in progress).
> The only question here is what should drive this machinery.. the tick
> probably.
> This shouldn't be too hard to do I think.
> Something a little like so perhaps?

I don’t think this will work. A CPU can go idle with lazy mm and nohz forever. This could lead to unbounded memory use on a lightly loaded system.

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