From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Kiryl Shutsemau <kas@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
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Hugh Dickins <hughd@google.com>, Qi Zheng <qi.zheng@linux.dev>
Subject: Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period
Date: Tue, 1 Sep 2026 18:14:08 +0100 [thread overview]
Message-ID: <apcH2jMKVfKtnppD@gremlin> (raw)
In-Reply-To: <apcFUthh0XSFg3JQ@thinkstation>
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:
> > > 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.
Great thanks! :)
>
> --
> Kiryl Shutsemau / Kirill A. Shutemov
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-09-01 17:14 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-01 11:01 [PATCH 00/12] mm: make userland page table freeing RCU-safe Lorenzo Stoakes (ARM)
2026-09-01 11:01 ` [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period Lorenzo Stoakes (ARM)
2026-09-01 11:18 ` sashiko-bot
2026-09-01 13:19 ` Kiryl Shutsemau
2026-09-01 14:12 ` Lorenzo Stoakes (ARM)
2026-09-01 14:24 ` Jason Gunthorpe
2026-09-01 14:41 ` Lorenzo Stoakes (ARM)
2026-09-01 15:28 ` Kiryl Shutsemau
2026-09-01 15:45 ` Lorenzo Stoakes (ARM)
2026-09-01 17:11 ` Kiryl Shutsemau
2026-09-01 17:14 ` Lorenzo Stoakes (ARM) [this message]
2026-09-01 15:54 ` Liam R. Howlett
2026-09-01 16:06 ` Jason Gunthorpe
2026-09-01 17:13 ` Kiryl Shutsemau
2026-09-01 17:47 ` Liam R. Howlett
2026-09-01 11:01 ` [PATCH 02/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for most 2-level architectures Lorenzo Stoakes (ARM)
2026-09-01 11:22 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 03/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU riscv Lorenzo Stoakes (ARM)
2026-09-01 11:14 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 04/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU arm Lorenzo Stoakes (ARM)
2026-09-01 11:18 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 05/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for arc, microblaze, xtensa Lorenzo Stoakes (ARM)
2026-09-01 11:28 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 06/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc64 Lorenzo Stoakes (ARM)
2026-09-01 11:23 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 07/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-coldfire Lorenzo Stoakes (ARM)
2026-09-01 11:23 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 08/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sh-X2 Lorenzo Stoakes (ARM)
2026-09-01 11:30 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola Lorenzo Stoakes (ARM)
2026-09-01 11:30 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 10/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc32 Lorenzo Stoakes (ARM)
2026-09-01 11:37 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 11/12] mm: make userland page table freeing RCU-safe Lorenzo Stoakes (ARM)
2026-09-01 11:52 ` sashiko-bot
2026-09-01 13:33 ` Kiryl Shutsemau
2026-09-01 14:03 ` Lorenzo Stoakes (ARM)
2026-09-01 11:01 ` [PATCH 12/12] mm: change the contract for free_pgtables(), update docs Lorenzo Stoakes (ARM)
2026-09-01 11:37 ` sashiko-bot
2026-09-01 13:57 ` Kiryl Shutsemau
2026-09-01 14:31 ` Lorenzo Stoakes (ARM)
2026-09-01 17:15 ` Kiryl Shutsemau
2026-09-01 17:25 ` Lorenzo Stoakes (ARM)
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