Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Date: 2026-09-01 17:14:41
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On Tue, Sep 01, 2026 at 06:11:57PM +0100, Kiryl Shutsemau wrote:
On Tue, Sep 01, 2026 at 04:45:14PM +0100, Lorenzo Stoakes (ARM) wrote:quoted
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.quoted
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.
Great thanks! :)
-- Kiryl Shutsemau / Kirill A. Shutemov
-- Cheers, Lorenzo