From 4265d67e405a41562634279ca1ededf79fdadcd7 Mon Sep 17 00:00:00 2001
From: Balbir Singh <balbirs@nvidia.com>
Date: Wed, 1 Oct 2025 16:57:02 +1000
Subject: mm/migrate_device: add THP splitting during migration
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Implement migrate_vma_split_pages() to handle THP splitting during the
migration process when destination cannot allocate compound pages.

This addresses the common scenario where migrate_vma_setup() succeeds with
MIGRATE_PFN_COMPOUND pages, but the destination device cannot allocate
large pages during the migration phase.

Key changes:
- migrate_vma_split_pages(): Split already-isolated pages during migration
- Enhanced folio_split() and __split_unmapped_folio() with isolated
  parameter to avoid redundant unmap/remap operations

This provides a fallback mechansim to ensure migration succeeds even when
large page allocation fails at the destination.

[matthew.brost@intel.com: add THP splitting during migration]
  Link: https://lkml.kernel.org/r/20251120230825.181072-2-matthew.brost@intel.com
Link: https://lkml.kernel.org/r/20251001065707.920170-12-balbirs@nvidia.com
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/huge_mm.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

(limited to 'include')

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 82408c90b396..ed99e6bd31ac 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -365,8 +365,8 @@ unsigned long thp_get_unmapped_area_vmflags(struct file *filp, unsigned long add
 		vm_flags_t vm_flags);
 
 bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins);
-int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
-		unsigned int new_order);
+int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
+		unsigned int new_order, bool unmapped);
 int min_order_for_split(struct folio *folio);
 int split_folio_to_list(struct folio *folio, struct list_head *list);
 bool uniform_split_supported(struct folio *folio, unsigned int new_order,
@@ -375,6 +375,13 @@ bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
 		bool warns);
 int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
 		struct list_head *list);
+
+static inline int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
+		unsigned int new_order)
+{
+	return __split_huge_page_to_list_to_order(page, list, new_order, false);
+}
+
 /*
  * try_folio_split_to_order - try to split a @folio at @page to @new_order using
  * non uniform split.
-- 
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