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(n7kwfhcd2z0e9u7cxfd-1.v6.elisa-mobile.fi. [2001:999:704:9310:43e6:e14c:406:e339]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-56e5c3b6002sm364013e87.28.2025.09.11.04.11.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 04:11:41 -0700 (PDT) Message-ID: <9047198d-7b35-435b-a933-ff7b1357919b@redhat.com> Date: Thu, 11 Sep 2025 14:11:40 +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: [v4 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: <20250903011900.3657435-1-balbirs@nvidia.com> <20250903011900.3657435-7-balbirs@nvidia.com> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <20250903011900.3657435-7-balbirs@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, On 9/3/25 04:18, 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 9009e27b5f44..40e1c792eb54 100644 > --- a/include/linux/migrate.h > +++ b/include/linux/migrate.h > @@ -134,6 +134,7 @@ 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) > @@ -152,6 +153,7 @@ 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 e58c3f9d01c8..aba0cd7856da 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 > for (addr = start; addr < end; addr += PAGE_SIZE) { > migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE; > migrate->dst[migrate->npages] = 0; > @@ -102,57 +120,150 @@ static int migrate_vma_split_folio(struct folio *folio, > return 0; > } --Mika