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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by MN1PEPF0000F0E0.mail.protection.outlook.com (10.167.242.38) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.181.6 via Frontend Transport; Tue, 30 Jun 2026 07:29:07 +0000 Received: from [127.0.1.1] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Tue, 30 Jun 2026 02:28:57 -0500 From: Shivank Garg Date: Tue, 30 Jun 2026 07:28:37 +0000 Subject: [PATCH RFC v6 1/5] mm/migrate: skip data copy for already-copied folios Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-ID: <20260630-shivank-batch-migrate-offload-v6-1-da95d7e8b8a2@amd.com> References: <20260630-shivank-batch-migrate-offload-v6-0-da95d7e8b8a2@amd.com> In-Reply-To: <20260630-shivank-batch-migrate-offload-v6-0-da95d7e8b8a2@amd.com> To: Andrew Morton , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , "Alistair Popple" , Lorenzo Stoakes , "Liam R. 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When set, it tells __migrate_folio() to skip folio_mc_copy() and perform metadata-only migration. This bit is not set yet, the batch-copy path enables it later in a subsequent patch. Update __migrate_folio_extract() to preserve FOLIO_CONTENT_COPIED while it consumes old states of src folio. Move the dst->migrate_info state enum to migrate.h header file so offload drivers can see FOLIO_CONTENT_COPIED. On 32Bit, we do not have spare bit to store FOLIO_CONTENT_COPIED info, migration copy offload is disabled for them. Signed-off-by: Shivank Garg --- include/linux/migrate.h | 25 +++++++++++++++++++++++++ mm/migrate.c | 29 +++++++++++++---------------- 2 files changed, 38 insertions(+), 16 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index d5af2b7f577b..876035df2fdc 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -72,6 +72,31 @@ int folio_migrate_mapping(struct address_space *mapping, struct folio *newfolio, struct folio *folio, int extra_count); int set_movable_ops(const struct movable_operations *ops, enum pagetype type); +/* + * To record some information during migration, we use the migrate_info + * field of struct folio of the newly allocated destination folio, + * together with the anon_vma pointer. The state is encoded in the + * unused low bits of the pointer. + * This is safe because nobody is using it except us. + * + * FOLIO_WAS_MAPPED and FOLIO_WAS_MLOCKED record the src folios's state + * at unmap time and are consumed during the move/undo phase. + * FOLIO_CONTENT_COPIED tells __migrate_folio() that the folio contents + * have already been copied, so the per-folio copy can be skipped. A + * driver must set this bit on each dst folio it copied. + */ +enum { + FOLIO_WAS_MAPPED = BIT(0), + FOLIO_WAS_MLOCKED = BIT(1), + FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED, +#ifdef CONFIG_64BIT + FOLIO_CONTENT_COPIED = BIT(2), +#else + /* On 32bit we do not have a spare bit, migration-copy offload is disabled. */ + FOLIO_CONTENT_COPIED = 0, +#endif +}; + #else static inline void putback_movable_pages(struct list_head *l) {} diff --git a/mm/migrate.c b/mm/migrate.c index 7a83032a14b5..b3f632575c82 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -859,14 +859,21 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst, enum migrate_mode mode) { int rc, expected_count = folio_expected_ref_count(src) + 1; + const bool already_copied = dst->migrate_info & FOLIO_CONTENT_COPIED; + + /* Consume the content copied marker */ + if (already_copied) + dst->migrate_info &= ~FOLIO_CONTENT_COPIED; /* Check whether src does not have extra refs before we do more work */ if (folio_ref_count(src) != expected_count) return -EAGAIN; - rc = folio_mc_copy(dst, src); - if (unlikely(rc)) - return rc; + if (!already_copied) { + rc = folio_mc_copy(dst, src); + if (unlikely(rc)) + return rc; + } rc = __folio_migrate_mapping(mapping, dst, src, expected_count); if (rc) @@ -1129,17 +1136,6 @@ static int move_to_new_folio(struct folio *dst, struct folio *src, return rc; } -/* - * To record some information during migration, we use the migrate_info - * field of struct folio of the newly allocated destination folio. - * This is safe because nobody is using it except us. - */ -enum { - FOLIO_WAS_MAPPED = BIT(0), - FOLIO_WAS_MLOCKED = BIT(1), - FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED, -}; - static void __migrate_folio_record(struct folio *dst, int old_folio_state, struct anon_vma *anon_vma) { @@ -1151,9 +1147,10 @@ static void __migrate_folio_extract(struct folio *dst, { unsigned long info = dst->migrate_info; - *anon_vmap = (struct anon_vma *)(info & ~FOLIO_OLD_STATES); + *anon_vmap = (struct anon_vma *)(info & ~(FOLIO_OLD_STATES | + FOLIO_CONTENT_COPIED)); *old_folio_state = info & FOLIO_OLD_STATES; - dst->migrate_info = 0; + dst->migrate_info &= FOLIO_CONTENT_COPIED; } /* Restore the source folio to the original state upon failure */ -- 2.43.0