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.
Cc: Andrew Morton <akpm@linux-foundation.org>
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: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
---
include/linux/huge_mm.h | 11 +++++--
lib/test_hmm.c | 9 ++++++
mm/huge_memory.c | 45 ++++++++++++++-------------
mm/migrate_device.c | 69 ++++++++++++++++++++++++++++++++++-------
4 files changed, 100 insertions(+), 34 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2c6a0c3c862c..3242a262b79e 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 - try to split a @folio at @page using non uniform split.
* @folio: folio to be split
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 41092c065c2d..6455707df902 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -1611,6 +1611,15 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
order = folio_order(page_folio(vmf->page));
nr = 1 << order;
+ /*
+ * When folios are partially mapped, we can't rely on the folio
+ * order of vmf->page as the folio might not be fully split yet
+ */
+ if (vmf->pte) {
+ order = 0;
+ nr = 1;
+ }
+
/*
* Consider a per-cpu cache of src and dst pfns, but with
* large number of cpus that might not scale well.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e38482e6e5c0..c69adc69c424 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3459,15 +3459,6 @@ static void __split_folio_to_order(struct folio *folio, int old_order,
new_folio->mapping = folio->mapping;
new_folio->index = folio->index + i;
- /*
- * page->private should not be set in tail pages. Fix up and warn once
- * if private is unexpectedly set.
- */
- if (unlikely(new_folio->private)) {
- VM_WARN_ON_ONCE_PAGE(true, new_head);
- new_folio->private = NULL;
- }
-
if (folio_test_swapcache(folio))
new_folio->swap.val = folio->swap.val + i;
@@ -3696,6 +3687,7 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
* @lock_at: a page within @folio to be left locked to caller
* @list: after-split folios will be put on it if non NULL
* @uniform_split: perform uniform split or not (non-uniform split)
+ * @unmapped: The pages are already unmapped, they are migration entries.
*
* It calls __split_unmapped_folio() to perform uniform and non-uniform split.
* It is in charge of checking whether the split is supported or not and
@@ -3711,7 +3703,7 @@ bool uniform_split_supported(struct folio *folio, unsigned int new_order,
*/
static int __folio_split(struct folio *folio, unsigned int new_order,
struct page *split_at, struct page *lock_at,
- struct list_head *list, bool uniform_split)
+ struct list_head *list, bool uniform_split, bool unmapped)
{
struct deferred_split *ds_queue = get_deferred_split_queue(folio);
XA_STATE(xas, &folio->mapping->i_pages, folio->index);
@@ -3761,13 +3753,15 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
* is taken to serialise against parallel split or collapse
* operations.
*/
- anon_vma = folio_get_anon_vma(folio);
- if (!anon_vma) {
- ret = -EBUSY;
- goto out;
+ if (!unmapped) {
+ anon_vma = folio_get_anon_vma(folio);
+ if (!anon_vma) {
+ ret = -EBUSY;
+ goto out;
+ }
+ anon_vma_lock_write(anon_vma);
}
mapping = NULL;
- anon_vma_lock_write(anon_vma);
} else {
unsigned int min_order;
gfp_t gfp;
@@ -3834,7 +3828,8 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
goto out_unlock;
}
- unmap_folio(folio);
+ if (!unmapped)
+ unmap_folio(folio);
/* block interrupt reentry in xa_lock and spinlock */
local_irq_disable();
@@ -3921,10 +3916,13 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
next = folio_next(new_folio);
+ zone_device_private_split_cb(folio, new_folio);
+
expected_refs = folio_expected_ref_count(new_folio) + 1;
folio_ref_unfreeze(new_folio, expected_refs);
- lru_add_split_folio(folio, new_folio, lruvec, list);
+ if (!unmapped)
+ lru_add_split_folio(folio, new_folio, lruvec, list);
/*
* Anonymous folio with swap cache.
@@ -3958,6 +3956,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
folio_put_refs(new_folio, nr_pages);
}
+ zone_device_private_split_cb(folio, NULL);
/*
* Unfreeze @folio only after all page cache entries, which
* used to point to it, have been updated with new folios.
@@ -3981,6 +3980,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
local_irq_enable();
+ if (unmapped)
+ return ret;
+
if (nr_shmem_dropped)
shmem_uncharge(mapping->host, nr_shmem_dropped);
@@ -4071,12 +4073,13 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
* Returns -EINVAL when trying to split to an order that is incompatible
* with the folio. Splitting to order 0 is compatible with all folios.
*/
-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)
{
struct folio *folio = page_folio(page);
- return __folio_split(folio, new_order, &folio->page, page, list, true);
+ return __folio_split(folio, new_order, &folio->page, page, list, true,
+ unmapped);
}
/*
@@ -4105,7 +4108,7 @@ int folio_split(struct folio *folio, unsigned int new_order,
struct page *split_at, struct list_head *list)
{
return __folio_split(folio, new_order, split_at, &folio->page, list,
- false);
+ false, false);
}
int min_order_for_split(struct folio *folio)
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 1dfcf4799ea5..32cb7355f525 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -910,6 +910,29 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
src[i] &= ~MIGRATE_PFN_MIGRATE;
return 0;
}
+
+static int migrate_vma_split_pages(struct migrate_vma *migrate,
+ unsigned long idx, unsigned long addr,
+ struct folio *folio)
+{
+ unsigned long i;
+ unsigned long pfn;
+ unsigned long flags;
+ int ret = 0;
+
+ folio_get(folio);
+ split_huge_pmd_address(migrate->vma, addr, true);
+ ret = __split_huge_page_to_list_to_order(folio_page(folio, 0), NULL,
+ 0, true);
+ if (ret)
+ return ret;
+ migrate->src[idx] &= ~MIGRATE_PFN_COMPOUND;
+ flags = migrate->src[idx] & ((1UL << MIGRATE_PFN_SHIFT) - 1);
+ pfn = migrate->src[idx] >> MIGRATE_PFN_SHIFT;
+ for (i = 1; i < HPAGE_PMD_NR; i++)
+ migrate->src[i+idx] = migrate_pfn(pfn + i) | flags;
+ return ret;
+}
#else /* !CONFIG_ARCH_ENABLE_THP_MIGRATION */
static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
unsigned long addr,
@@ -919,6 +942,13 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
{
return 0;
}
+
+static int migrate_vma_split_pages(struct migrate_vma *migrate,
+ unsigned long idx, unsigned long addr,
+ struct folio *folio)
+{
+ return 0;
+}
#endif
/*
@@ -1068,8 +1098,9 @@ static void __migrate_device_pages(unsigned long *src_pfns,
struct migrate_vma *migrate)
{
struct mmu_notifier_range range;
- unsigned long i;
+ unsigned long i, j;
bool notified = false;
+ unsigned long addr;
for (i = 0; i < npages; ) {
struct page *newpage = migrate_pfn_to_page(dst_pfns[i]);
@@ -1111,12 +1142,16 @@ static void __migrate_device_pages(unsigned long *src_pfns,
(!(dst_pfns[i] & MIGRATE_PFN_COMPOUND))) {
nr = HPAGE_PMD_NR;
src_pfns[i] &= ~MIGRATE_PFN_COMPOUND;
- src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
- goto next;
+ } else {
+ nr = 1;
}
- migrate_vma_insert_page(migrate, addr, &dst_pfns[i],
- &src_pfns[i]);
+ for (j = 0; j < nr && i + j < npages; j++) {
+ src_pfns[i+j] |= MIGRATE_PFN_MIGRATE;
+ migrate_vma_insert_page(migrate,
+ addr + j * PAGE_SIZE,
+ &dst_pfns[i+j], &src_pfns[i+j]);
+ }
goto next;
}
@@ -1138,7 +1173,14 @@ static void __migrate_device_pages(unsigned long *src_pfns,
MIGRATE_PFN_COMPOUND);
goto next;
}
- src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+ nr = 1 << folio_order(folio);
+ addr = migrate->start + i * PAGE_SIZE;
+ if (migrate_vma_split_pages(migrate, i, addr,
+ folio)) {
+ src_pfns[i] &= ~(MIGRATE_PFN_MIGRATE |
+ MIGRATE_PFN_COMPOUND);
+ goto next;
+ }
} else if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) &&
(dst_pfns[i] & MIGRATE_PFN_COMPOUND) &&
!(src_pfns[i] & MIGRATE_PFN_COMPOUND)) {
@@ -1174,11 +1216,16 @@ static void __migrate_device_pages(unsigned long *src_pfns,
if (migrate && migrate->fault_page == page)
extra_cnt = 1;
- r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt);
- if (r)
- src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
- else
- folio_migrate_flags(newfolio, folio);
+ for (j = 0; j < nr && i + j < npages; j++) {
+ folio = page_folio(migrate_pfn_to_page(src_pfns[i+j]));
+ newfolio = page_folio(migrate_pfn_to_page(dst_pfns[i+j]));
+
+ r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt);
+ if (r)
+ src_pfns[i+j] &= ~MIGRATE_PFN_MIGRATE;
+ else
+ folio_migrate_flags(newfolio, folio);
+ }
next:
i += nr;
}
--
2.50.1
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