Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period

On Tue, Sep 01, 2026 at 04:45:14PM +0100, Lorenzo Stoakes (ARM) wrote:

quoted

munmap() of 64G worth of THP should be enough to demonstrate the
problem.

I mean you're going to hit that from RCU freeing page tables already, which
most architectures already do right?

Not at the same rate -- tlb_remove_table() batches into struct
mmu_table_batch. One call_rcu() per MAX_TABLE_BATCH.

So if RCU saturation is a problem, that problem already exists, but I've
not heard of that being a problem at all?

I did quick test and I don't see a measurable difference in munmap()
wall time of 40G of THPs. I see ~17x more softirqs, but this is
expected.

The objection is retracted.

We can return to this later if it is going to be visible anywhere.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov