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b=CGwxpnBELT2SBdYqTWoImYAwOQE6VH3Z/GK/BjARDqL1OwqOg0mgW0LKYZbEz6KG/ SAEdW0C3XoQlNf/Suzav0R/znaJUw+Zx9A2mbHr2oOXegJenEJuYHoxqO8iDkDY1Z9 1biQcQdcVJCtdUNP3yYInn6yCqUpVeK7z7C2EAovrzfdZBjcL/JFpIALGaFmJaradQ K2j9jnOfTmkKmmk84SVrHosCBrgboNIbijZzR8QL5Fqh44ddhSMmY5yz0y1urmxGHS 6q7CoSukBqGFsgY4TVNW9UMehwhIHeIFxPbMVn2h2JoaMn82yQAVpHyoBvs8ilNbAC LQ/yguM0me+uQ== Message-ID: <73625017-b944-446b-95b6-6c586c304f35@kernel.org> Date: Tue, 29 Sep 2026 10:43:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 03/12] mm/sparse-vmemmap: introduce CONFIG_VMEMMAP_OPTIMIZATION To: Muchun Song Cc: Muchun Song , Andrew Morton , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Randy Dunlap , Lance Yang References: <20260927025441.741633-1-songmuchun@bytedance.com> <20260927025441.741633-4-songmuchun@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0FCB54000B X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: ojxxjg6nc3rzw38wyqabb5prwaxc46wu X-HE-Tag: 1790671387-610022 X-HE-Meta: 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 k4gruKFS TX46Kk63YtCp36vqkgzEskj/I7Yt+4/Lqcbb0d0FrNtgyKSSrNOyv0n44Zl3f07O+JEhf7cpszQZsr0hNR+5KbkakAQ9nwaOjSevOlWBG6WTvQ0b7OXq50/MtCm9NsqKymeRRzBye8FzKislkWlyRU253l0BaletBdkAUjJI0WP0exAO5JxJ/pbAlfryM4TMYj56UiklattiBKK9k9yc146MgMQyNMW4u5xZKoHpC3P1KB42WX1BI11bMt+vlbQqHNdHL5qirvCGQAlBT1UGHGQMtZelAm7CKoitHOHlCmQedHnCkhEJE7Gl+PosBjjAK2V70+IB/Tkjxg54HcXLp1MnGXdyRgjYqhtVF Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/29/26 09:53, Muchun Song wrote: > > >> On Sep 29, 2026, at 15:11, David Hildenbrand (Arm) wrote: >> >> On 9/27/26 04:54, Muchun Song wrote: >>> The section-based vmemmap optimization infrastructure is guarded by >>> CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP, but it can also be used by >>> ZONE_DEVICE users that set dev_pagemap::vmemmap_shift. Introduce >>> CONFIG_VMEMMAP_OPTIMIZATION as a common config for the shared >>> infrastructure. >>> >>> Select the new option from HUGETLB_PAGE_OPTIMIZE_VMEMMAP and from >>> ZONE_DEVICE when the architecture opts in to DAX vmemmap optimization, >>> and use it to guard the generic sparse-vmemmap state and helpers. >>> >>> Signed-off-by: Muchun Song >>> Acked-by: Qi Zheng >>> Acked-by: Mike Rapoport (Microsoft) >>> --- >>> v5: >>> - Move this patch after the shared tail-page factoring. >>> - Select VMEMMAP_OPTIMIZATION from ZONE_DEVICE instead of DEV_DAX, >>> covering all users of dev_pagemap::vmemmap_shift, reported by >>> Sashiko. >>> >>> v4: >>> - Rename SPARSEMEM_VMEMMAP_OPTIMIZATION to VMEMMAP_OPTIMIZATION >>> (suggested by Mike Rapoport) >>> - Collect Acked-by from Mike Rapoport >>> >>> v2: >>> - Fix SPARSEMEM_VMEMMAP_OPTIMIZATION being selected without SPARSEMEM_VMEMMAP >>> reported by Sashiko. >>> - Add an explicit DEV_DAX dependency on ZONE_DEVICE >>> - Collect Acked-by from Qi Zheng >>> --- >>> arch/x86/entry/vdso/vdso32/fake_32bit_build.h | 2 +- >>> fs/Kconfig | 1 + >>> include/linux/mm.h | 3 +++ >>> include/linux/mmzone.h | 10 +++++----- >>> include/linux/page-flags.h | 5 ++--- >>> mm/Kconfig | 5 +++++ >>> mm/sparse-vmemmap.c | 2 +- >>> mm/sparse.h | 6 +++--- >>> 8 files changed, 21 insertions(+), 13 deletions(-) >>> >>> diff --git a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h b/arch/x86/entry/vdso/vdso32/fake_32bit_build.h >>> index bc3e549795c3..72a92cb9b53d 100644 >>> --- a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h >>> +++ b/arch/x86/entry/vdso/vdso32/fake_32bit_build.h >>> @@ -11,7 +11,7 @@ >>> #undef CONFIG_PGTABLE_LEVELS >>> #undef CONFIG_ILLEGAL_POINTER_VALUE >>> #undef CONFIG_SPARSEMEM_VMEMMAP >>> -#undef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP >>> +#undef CONFIG_VMEMMAP_OPTIMIZATION >>> #undef CONFIG_NR_CPUS >>> #undef CONFIG_PARAVIRT_XXL >>> >>> diff --git a/fs/Kconfig b/fs/Kconfig >>> index d1c210c6508f..1454b7fe9641 100644 >>> --- a/fs/Kconfig >>> +++ b/fs/Kconfig >>> @@ -278,6 +278,7 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP >>> def_bool HUGETLB_PAGE >>> depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP >>> depends on SPARSEMEM_VMEMMAP >>> + select VMEMMAP_OPTIMIZATION >> >> Acked-by: David Hildenbrand (Arm) > > Thanks. > >> >> Is there a path to remove HUGETLB_PAGE_OPTIMIZE_VMEMMAP, and to merge >> ARCH_WANT_OPTIMIZE_DAX_VMEMMAP+ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP into a >> ARCH_SUPPORTS_VMEMMAP_OPTIMIZATION? > > These are actually two completely different capabilities. > > ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP requires the architecture > to support dynamic updates to vmemmap page tables, meaning a > PTE entry can be changed from one valid entry to another > valid entry. This does not meet the requirements on arm64, > because arm64 requires page table operations to satisfy BBM > (there is, of course, a series [1] attempting to do this). > > However, for ARCH_WANT_OPTIMIZE_DAX_VMEMMAP, the vmemmap page > tables do not involve dynamic updates, so the BBM requirement > can be satisfied. Therefore, arm64 can enable > ARCH_WANT_OPTIMIZE_DAX_VMEMMAP, but cannot enable > ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP. To make the naming clearer, > I have another patch [2] that renames it for greater clarity. Ah, perfect. Too many patches floating around :) I thought there is a patch set to avoid the BBM requirement on arm64 from James, though. So not sure if both things will always stay separate. > > As for ARCH_WANT_OPTIMIZE_DAX_VMEMMAP, I plan to remove it > entirely in the future, because architectures that do not support > it can simply choose to disable it, as can be seen in patch [3]. > > So in my plan, ultimately only one config will remain: > ARCH_SUPPORTS_VMEMMAP_REMAP. > > I hope this clarifies the plan. Let me know what you think. Yes, thanks. -- Cheers, David