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(n4ctkw60s7hbahed3xa-1.v6.elisa-mobile.fi. [2001:999:408:6576:1142:7350:b6c5:671e]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-34f15a591fasm6136911fa.9.2025.09.11.22.28.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 22:28:33 -0700 (PDT) Message-ID: <4cc2ba18-e7de-448f-aaee-043ed68dc6e3@redhat.com> Date: Fri, 12 Sep 2025 08:28:32 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v5 06/15] mm/migrate_device: implement THP migration of zone device pages To: Balbir Singh , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: damon@lists.linux.dev, dri-devel@lists.freedesktop.org, Andrew Morton , David Hildenbrand , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , Matthew Brost , Francois Dugast References: <20250908000448.180088-1-balbirs@nvidia.com> <20250908000448.180088-7-balbirs@nvidia.com> <49039b9d-4c42-480f-a219-daf0958be28e@nvidia.com> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <49039b9d-4c42-480f-a219-daf0958be28e@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 9/12/25 08:04, Balbir Singh wrote: > On 9/11/25 21:52, Mika Penttilä wrote: >> sending again for the v5 thread.. >> >> On 9/8/25 03:04, Balbir Singh wrote: >> >>> MIGRATE_VMA_SELECT_COMPOUND will be used to select THP pages during >>> migrate_vma_setup() and MIGRATE_PFN_COMPOUND will make migrating >>> device pages as compound pages during device pfn migration. >>> >>> migrate_device code paths go through the collect, setup >>> and finalize phases of migration. >>> >>> The entries in src and dst arrays passed to these functions still >>> remain at a PAGE_SIZE granularity. When a compound page is passed, >>> the first entry has the PFN along with MIGRATE_PFN_COMPOUND >>> and other flags set (MIGRATE_PFN_MIGRATE, MIGRATE_PFN_VALID), the >>> remaining entries (HPAGE_PMD_NR - 1) are filled with 0's. This >>> representation allows for the compound page to be split into smaller >>> page sizes. >>> >>> migrate_vma_collect_hole(), migrate_vma_collect_pmd() are now THP >>> page aware. Two new helper functions migrate_vma_collect_huge_pmd() >>> and migrate_vma_insert_huge_pmd_page() have been added. >>> >>> migrate_vma_collect_huge_pmd() can collect THP pages, but if for >>> some reason this fails, there is fallback support to split the folio >>> and migrate it. >>> >>> migrate_vma_insert_huge_pmd_page() closely follows the logic of >>> migrate_vma_insert_page() >>> >>> Support for splitting pages as needed for migration will follow in >>> later patches in this series. >>> >>> Cc: Andrew Morton >>> Cc: David Hildenbrand >>> Cc: Zi Yan >>> Cc: Joshua Hahn >>> Cc: Rakie Kim >>> Cc: Byungchul Park >>> Cc: Gregory Price >>> Cc: Ying Huang >>> Cc: Alistair Popple >>> Cc: Oscar Salvador >>> Cc: Lorenzo Stoakes >>> Cc: Baolin Wang >>> Cc: "Liam R. Howlett" >>> Cc: Nico Pache >>> Cc: Ryan Roberts >>> Cc: Dev Jain >>> Cc: Barry Song >>> Cc: Lyude Paul >>> Cc: Danilo Krummrich >>> Cc: David Airlie >>> Cc: Simona Vetter >>> Cc: Ralph Campbell >>> Cc: Mika Penttilä >>> Cc: Matthew Brost >>> Cc: Francois Dugast >>> >>> Signed-off-by: Balbir Singh >>> --- >>> include/linux/migrate.h | 2 + >>> mm/migrate_device.c | 456 ++++++++++++++++++++++++++++++++++------ >>> 2 files changed, 395 insertions(+), 63 deletions(-) >>> >>> diff --git a/include/linux/migrate.h b/include/linux/migrate.h >>> index 1f0ac122c3bf..41b4cc05a450 100644 >>> --- a/include/linux/migrate.h >>> +++ b/include/linux/migrate.h >>> @@ -125,6 +125,7 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node) >>> #define MIGRATE_PFN_VALID (1UL << 0) >>> #define MIGRATE_PFN_MIGRATE (1UL << 1) >>> #define MIGRATE_PFN_WRITE (1UL << 3) >>> +#define MIGRATE_PFN_COMPOUND (1UL << 4) >>> #define MIGRATE_PFN_SHIFT 6 >>> >>> static inline struct page *migrate_pfn_to_page(unsigned long mpfn) >>> @@ -143,6 +144,7 @@ enum migrate_vma_direction { >>> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0, >>> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1, >>> MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2, >>> + MIGRATE_VMA_SELECT_COMPOUND = 1 << 3, >>> }; >>> >>> struct migrate_vma { >>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>> index f45ef182287d..1dfcf4799ea5 100644 >>> --- a/mm/migrate_device.c >>> +++ b/mm/migrate_device.c >>> @@ -14,6 +14,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include "internal.h" >>> >>> @@ -44,6 +45,23 @@ static int migrate_vma_collect_hole(unsigned long start, >>> if (!vma_is_anonymous(walk->vma)) >>> return migrate_vma_collect_skip(start, end, walk); >>> >>> + if (thp_migration_supported() && >>> + (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && >>> + (IS_ALIGNED(start, HPAGE_PMD_SIZE) && >>> + IS_ALIGNED(end, HPAGE_PMD_SIZE))) { >>> + migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE | >>> + MIGRATE_PFN_COMPOUND; >>> + migrate->dst[migrate->npages] = 0; >>> + migrate->npages++; >>> + migrate->cpages++; >>> + >>> + /* >>> + * Collect the remaining entries as holes, in case we >>> + * need to split later >>> + */ >>> + return migrate_vma_collect_skip(start + PAGE_SIZE, end, walk); >>> + } >>> + >> seems you have to split_huge_pmd() for the huge zero page here in case >> of !thp_migration_supported() afaics >> > Not really, if pfn is 0, we do a vm_insert_page (please see if (!page) line 1107) and > folio handling in migrate_vma_finalize line 1284 Ok actually seems it is handled by migrate_vma_insert_page() which does if (!pmd_none(*pmdp)) { if (pmd_trans_huge(*pmdp)) { if (!is_huge_zero_pmd(*pmdp)) goto abort; folio_get(pmd_folio(*pmdp)); split_huge_pmd(vma, pmdp, addr); <----- here } else if (pmd_leaf(*pmdp)) goto abort; } > > Thanks, > Balbir > --Mika