From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>, Zi Yan <ziy@nvidia.com>,
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Subject: Re: [PATCH v4 00/12] mm: make userland page table freeing RCU-safe
Date: Wed, 23 Sep 2026 08:04:25 +0100 [thread overview]
Message-ID: <arN3iaw7VDIA-bWf@gremlin> (raw)
In-Reply-To: <20260922160021.a2fc65d05d9b867a141e5457@linux-foundation.org>
On Tue, Sep 22, 2026 at 04:00:21PM -0700, Andrew Morton wrote:
> On Tue, 22 Sep 2026 16:35:31 +0100 "Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote:
>
> > The majority of architectures in the kernel defer page table freeing until
> > an RCU grace period has elapsed, this series converts all remaining
> > architectures to do so too and eliminates CONFIG_MMU_GATHER_RCU_TABLE_FREE
> > altogether.
> >
> > This is important because it enables safe lockless page table walking under
> > RCU alone.
>
> Do we have reason to believe that anyone is seeing any effects from
> their arch's failure to rcu-free the page tables?
We have reason to believe that it completely blocks other work like
scalable CoW :)
>
> This sounds like a rather long-standing wart, yes?
Not really, if you read the cover letter you can see the history of people
working on this, this is the final piece of the puzzle and despite the
rather muted reception this change is a big deal (TM).
>
> The patchset is thinly reviewed and mm.git is bursting at the seams
> again. I'll play wait-and-see on this series. Feel free to cluebat me
> if that's a bad call.
Err, Kiryl reviewed the entire series, I sent it in -rc1 of this cycle, and
it's been in -next forever?
Lance is reviewing now, presumably maybe David will review based on the
fact I updated on his feedback to _expand_ some functionality here.
So I'd argue this is contender for one of the top priority series for this
cycle, actually! [and is CRITICAL for my scalable CoW work, easily the most
important this cycle]
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-09-23 7:04 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-22 15:35 Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 01/12] mm/khugepaged: deposit a newly allocated page table on collapse Lorenzo Stoakes (ARM)
2026-09-23 2:24 ` Lance Yang
2026-09-23 7:09 ` Lorenzo Stoakes (ARM)
2026-09-23 7:14 ` Lorenzo Stoakes (ARM)
2026-09-23 7:24 ` Lance Yang
2026-09-23 19:53 ` Andrew Morton
2026-09-24 3:28 ` Baolin Wang
2026-09-23 8:54 ` David Hildenbrand (Arm)
2026-09-23 9:00 ` Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 02/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for most 2-level architectures Lorenzo Stoakes (ARM)
2026-09-23 4:39 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 03/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU riscv Lorenzo Stoakes (ARM)
2026-09-23 6:15 ` Lance Yang
2026-09-23 7:05 ` Lorenzo Stoakes (ARM)
2026-09-23 7:17 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 04/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU arm Lorenzo Stoakes (ARM)
2026-09-23 8:05 ` Lance Yang
2026-09-23 8:15 ` Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 05/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for arc, microblaze, xtensa Lorenzo Stoakes (ARM)
2026-09-23 8:43 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 06/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc64 Lorenzo Stoakes (ARM)
2026-09-23 8:54 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 07/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-coldfire Lorenzo Stoakes (ARM)
2026-09-23 9:13 ` Lance Yang
2026-09-23 11:31 ` Greg Ungerer
2026-09-23 11:36 ` Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 08/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sh-X2 Lorenzo Stoakes (ARM)
2026-09-23 11:54 ` Lance Yang
2026-09-23 11:56 ` Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola Lorenzo Stoakes (ARM)
2026-09-23 13:16 ` Lance Yang
2026-09-23 13:21 ` Lorenzo Stoakes (ARM)
2026-09-22 15:35 ` [PATCH v4 10/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc32 Lorenzo Stoakes (ARM)
2026-09-24 2:41 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 11/12] mm: make userland page table freeing RCU-safe Lorenzo Stoakes (ARM)
2026-09-23 9:04 ` David Hildenbrand (Arm)
2026-09-23 9:06 ` Lorenzo Stoakes (ARM)
2026-09-23 9:13 ` David Hildenbrand (Arm)
2026-09-23 11:48 ` Lorenzo Stoakes (ARM)
2026-09-23 13:38 ` David Hildenbrand (Arm)
2026-09-23 13:43 ` Lorenzo Stoakes (ARM)
2026-09-24 2:55 ` Lance Yang
2026-09-22 15:35 ` [PATCH v4 12/12] mm: change the contract for free_pgtables(), update docs Lorenzo Stoakes (ARM)
2026-09-23 9:08 ` David Hildenbrand (Arm)
2026-09-23 11:55 ` Lorenzo Stoakes (ARM)
2026-09-24 3:26 ` Lance Yang
2026-09-22 16:42 ` [PATCH v4 00/12] mm: make userland page table freeing RCU-safe Matthew Wilcox
2026-09-22 17:22 ` Lorenzo Stoakes (ARM)
2026-09-22 23:00 ` Andrew Morton
2026-09-23 7:04 ` Lorenzo Stoakes (ARM) [this message]
2026-09-23 20:01 ` Andrew Morton
2026-09-23 8:45 ` David Hildenbrand (Arm)
2026-09-23 9:04 ` Lorenzo Stoakes (ARM)
2026-09-23 9:15 ` David Hildenbrand (Arm)
2026-09-23 9:39 ` Vlastimil Babka (SUSE)
2026-09-23 11:39 ` Lorenzo Stoakes (ARM)
2026-09-23 19:59 ` Andrew Morton
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