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mm/sparse-vmemmap: introduce CONFIG_VMEMMAP_OPTIMIZATION From: Muchun Song In-Reply-To: <20260916083627.2145779-1-songmuchun@bytedance.com> Date: Wed, 16 Sep 2026 16:45:57 +0800 Cc: David Hildenbrand , Muchun Song , 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 Content-Transfer-Encoding: quoted-printable Message-Id: <6A2BDF6D-96D2-4771-AB3F-7E702B01FFF2@linux.dev> References: <20260916064341.1825793-2-songmuchun@bytedance.com> <20260916083627.2145779-1-songmuchun@bytedance.com> To: Andrew Morton X-Mailer: Apple Mail (2.3864.700.51.1.1) X-Rspam-User: X-Stat-Signature: bo44x1i7mtcjgz7ao55h6arjjpsyfeod X-Rspamd-Queue-Id: 0ED38A0002 X-Rspamd-Server: rspam07 X-HE-Tag: 1789548380-514793 X-HE-Meta: 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 zYzDRjTc wNS7t/hanitOtGRm53PEI7RdAJ3hqJvIRltFfxSBhb1Z/l9hd79OVBWC7fcDQOL44+OwaiXaK/gdkpwmWkJgXN9P3GQEvJSZUFmKowZbJnvZ+v7yz5AGMfkh4RLEl33UcUFTy6ZWCRhaFPrmkzo+Ay3KVI4li0+Xnsxi+bLKFOCfTbP0FhKFTVRE3xpwOYJAKYxYV1EZpLcr27UQUR4+ylRgzaCPxdR3oJCaGWZvpFmpZ7BjhLHu+sJ0rrLjJ+2aehwHDi+KXwTqIN2DU8TeOY+yO0nM9HxTKLoRZzBrydaK6NK46PsmQWzMwBGQ7hG/cFhexoeW3yRPrOq1K90psvjlsZm03iQc2KOpBWFebkCWbRxVURlQUMlX+YcaZiEScN+DoaU8x308BmN1oDMAxneThETyplQ8sSy9hvwMOyn78n7iONCdw5g0xiwFJ0IAdyWUVagw6OoIe0nM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Sep 16, 2026, at 16:36, Muchun Song = wrote: >=20 > 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. >=20 > 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. >=20 > Signed-off-by: Muchun Song > Acked-by: Qi Zheng > Acked-by: Mike Rapoport (Microsoft) > --- > Note: When folding this fix into > "mm/sparse-vmemmap: introduce CONFIG_VMEMMAP_OPTIMIZATION", > please use this commit message for the resulting patch. Hi Andrew, Sashiko found a configuration issue in patch 1 [1]. MSHV_VTL sets a non-zero dev_pagemap::vmemmap_shift for VTL0 memory. However, VMEMMAP_OPTIMIZATION is currently selected only by DEV_DAX or HUGETLB_PAGE_OPTIMIZE_VMEMMAP. With ZONE_DEVICE=3Dy and MSHV_VTL=3Dy, but DEV_DAX=3Dn and HUGETLB_PAGE=3Dn, VMEMMAP_OPTIMIZATION is therefore disabled. __vmemmap_can_optimize() always returns false in this configuration, so VTL0 memory uses an unoptimized vmemmap despite its non-zero vmemmap_shift. On common x86-64 configurations, this can consume up to about 1.5% of the mapped VTL0 memory for vmemmap metadata. The report is correct. The fixup in the parent message moves the conditional selection of VMEMMAP_OPTIMIZATION from DEV_DAX to ZONE_DEVICE. This covers every ZONE_DEVICE user that sets dev_pagemap::vmemmap_shift while retaining the architecture opt-in through ARCH_WANT_OPTIMIZE_DAX_VMEMMAP. It also removes the DEV_DAX dependency on ZONE_DEVICE that patch 1 added solely to satisfy the Kconfig dependency of VMEMMAP_OPTIMIZATION. Andrew, could you please fold this fixup into patch 1, "mm/sparse-vmemmap: introduce CONFIG_VMEMMAP_OPTIMIZATION"? [1] = https://sashiko.dev/#/patchset/20260916064341.1825793-1-songmuchun%40byted= ance.com Thanks, Muchun=