From: SeongJae Park <sj@kernel.org>
To: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Cc: SeongJae Park <sj@kernel.org>,
akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com,
david@kernel.org, ljs@kernel.org, surenb@google.com,
vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com,
corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com,
pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com,
usama.arif@linux.dev, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kselftest@vger.kernel.org, kvm@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH 01/14] mm: decouple protnone helpers from CONFIG_NUMA_BALANCING
Date: Wed, 29 Apr 2026 21:47:02 -0700 [thread overview]
Message-ID: <20260430044703.77862-1-sj@kernel.org> (raw)
In-Reply-To: <20260427114607.4068647-2-kas@kernel.org>
On Mon, 27 Apr 2026 12:45:49 +0100 "Kiryl Shutsemau (Meta)" <kas@kernel.org> wrote:
> pte_protnone() and pmd_protnone() detect present-but-inaccessible page
> table entries. This capability is useful beyond NUMA balancing — for
> example, userfaultfd working set tracking uses protnone PTEs to track
> page access without unmapping pages.
I agree. It can be useful for general access monitoring. I'm also slowly but
continuously working [1] to use that for DAMON.
>
> Introduce CONFIG_ARCH_HAS_PTE_PROTNONE to decouple the protnone PTE
> infrastructure from CONFIG_NUMA_BALANCING. The six architectures that
> support protnone PTEs (x86_64, arm64, powerpc, s390, riscv, loongarch)
> now select this option, and CONFIG_NUMA_BALANCING depends on it.
>
> No functional change — the same set of architectures continues to have
> working protnone support, but the infrastructure is now available
> independently of NUMA balancing.
I think this is a good change for making the infrastructure available for uffd.
I believe this can also be useful for making it further available for general
access monitoring purposes. I hope this to be landed on the mainline sooner
than later. Thank you for doing this, Kiryl!
>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> Assisted-by: Claude:claude-opus-4-6
Acked-by: SeongJae Park <sj@kernel.org>
[1] https://lore.kernel.org/linux-mm/20260218054320.4570-1-sj@kernel.org/
Thanks,
SJ
[...]
next prev parent reply other threads:[~2026-04-30 4:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 11:45 [PATCH 00/14] userfaultfd: working set tracking for VM guest memory Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 01/14] mm: decouple protnone helpers from CONFIG_NUMA_BALANCING Kiryl Shutsemau (Meta)
2026-04-30 4:47 ` SeongJae Park [this message]
2026-04-27 11:45 ` [PATCH 02/14] mm: rename uffd-wp PTE bit macros to uffd Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 03/14] mm: rename uffd-wp PTE accessors " Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 04/14] mm: add VM_UFFD_RWP VMA flag Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 05/14] mm: add MM_CP_UFFD_RWP change_protection() flag Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 06/14] mm: preserve RWP marker across PTE rewrites Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 07/14] mm: handle VM_UFFD_RWP in khugepaged, rmap, and GUP Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 08/14] userfaultfd: add UFFDIO_REGISTER_MODE_RWP and UFFDIO_RWPROTECT plumbing Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 09/14] mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 10/14] mm/pagemap: add PAGE_IS_ACCESSED for RWP tracking Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 11/14] userfaultfd: add UFFD_FEATURE_RWP_ASYNC for async fault resolution Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 12/14] userfaultfd: add UFFDIO_SET_MODE for runtime sync/async toggle Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 13/14] selftests/mm: add userfaultfd RWP tests Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 14/14] Documentation/userfaultfd: document RWP working set tracking Kiryl Shutsemau (Meta)
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