It was later reproduced on the same machine without huge pages enabled. PICNIC?

Yes, I did reproduce it (to a much smaller degree, but it's just a 48c/96t machine). But it's an absurd workload in an insane configuration. Not using huge pages hurts way more than the regression due to PREEMPT_LAZY does.

With what we know so far, I expect that there are just about no real world workloads that aren't already completely falling over that will be affected.

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pgaddict 5 hours ago | parent [-]

So why does it happen only with hugepages? Is the extra overhead / TLB pressure enough to trigger the issue in some way? Of is it because the regular pages get swapped out (which hugepages can't be)?

	▲	anarazel 5 hours ago \| parent [-]
		I don't fully know, but I suspect it's just that due to the minor faults and tlb misses there is terrible contention with the spinlock, regardless of the PREEMPT_LAZY when using 4k pages (that easily reproducible). Which is then made worse by preempting more with the lock held.