On 08.09.25 02:04, Balbir Singh wrote:
Implement CPU fault handling for zone device THP entries through
do_huge_pmd_device_private(), enabling transparent migration of
device-private large pages back to system memory on CPU access.
When the CPU accesses a zone device THP entry, the fault handler
calls the device driver's migrate_to_ram() callback to migrate
the entire large page back to system memory.
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: David Hildenbrand <da...@redhat.com>
Cc: Zi Yan <z...@nvidia.com>
Cc: Joshua Hahn <joshua.hah...@gmail.com>
Cc: Rakie Kim <rakie....@sk.com>
Cc: Byungchul Park <byungc...@sk.com>
Cc: Gregory Price <gou...@gourry.net>
Cc: Ying Huang <ying.hu...@linux.alibaba.com>
Cc: Alistair Popple <apop...@nvidia.com>
Cc: Oscar Salvador <osalva...@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
Cc: Baolin Wang <baolin.w...@linux.alibaba.com>
Cc: "Liam R. Howlett" <liam.howl...@oracle.com>
Cc: Nico Pache <npa...@redhat.com>
Cc: Ryan Roberts <ryan.robe...@arm.com>
Cc: Dev Jain <dev.j...@arm.com>
Cc: Barry Song <bao...@kernel.org>
Cc: Lyude Paul <ly...@redhat.com>
Cc: Danilo Krummrich <d...@kernel.org>
Cc: David Airlie <airl...@gmail.com>
Cc: Simona Vetter <sim...@ffwll.ch>
Cc: Ralph Campbell <rcampb...@nvidia.com>
Cc: Mika Penttilä <mpent...@redhat.com>
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: Francois Dugast <francois.dug...@intel.com>
Signed-off-by: Balbir Singh <balb...@nvidia.com>
---
include/linux/huge_mm.h | 7 +++++++
mm/huge_memory.c | 36 ++++++++++++++++++++++++++++++++++++
mm/memory.c | 6 ++++--
3 files changed, 47 insertions(+), 2 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 23f124493c47..2c6a0c3c862c 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -496,6 +496,8 @@ static inline bool folio_test_pmd_mappable(struct folio
*folio)
vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf);
+vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf);
+
extern struct folio *huge_zero_folio;
extern unsigned long huge_zero_pfn;
@@ -675,6 +677,11 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
return 0;
}
+static inline vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf)
+{
Is this a VM_WARN_ON_ONCE() or similar? (Maybe BUILD_BUG is possible?)
+ return 0;
+}
+
static inline bool is_huge_zero_folio(const struct folio *folio)
{
return false;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b720870c04b2..d634b2157a56 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1287,6 +1287,42 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct
vm_fault *vmf)
}
+vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ vm_fault_t ret = 0;
+ spinlock_t *ptl;
+ swp_entry_t swp_entry;
+ struct page *page;
+
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+ vma_end_read(vma);
+ return VM_FAULT_RETRY;
+ }
+
+ ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+ if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd))) {
+ spin_unlock(ptl);
+ return 0;
+ }
+
+ swp_entry = pmd_to_swp_entry(vmf->orig_pmd);
+ page = pfn_swap_entry_to_page(swp_entry);
+ vmf->page = page;
+ vmf->pte = NULL;
+ if (trylock_page(vmf->page)) {
+ get_page(page);
+ spin_unlock(ptl);
+ ret = page_pgmap(page)->ops->migrate_to_ram(vmf);
+ unlock_page(vmf->page);
+ put_page(page);
+ } else {
+ spin_unlock(ptl);
+ }
+
+ return ret;
+}
+
/*
* always: directly stall for all thp allocations
* defer: wake kswapd and fail if not immediately available
diff --git a/mm/memory.c b/mm/memory.c
index d9de6c056179..860665f4b692 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6298,8 +6298,10 @@ static vm_fault_t __handle_mm_fault(struct
vm_area_struct *vma,
vmf.orig_pmd = pmdp_get_lockless(vmf.pmd);
if (unlikely(is_swap_pmd(vmf.orig_pmd))) {
- VM_BUG_ON(thp_migration_supported() &&
-
!is_pmd_migration_entry(vmf.orig_pmd));
+ if (is_device_private_entry(
+ pmd_to_swp_entry(vmf.orig_pmd)))
Single line please.
But didn't we have a pmd helper for that?
+ return do_huge_pmd_device_private(&vmf);
+
if (is_pmd_migration_entry(vmf.orig_pmd))
pmd_migration_entry_wait(mm, vmf.pmd);
return 0;
--
Cheers
David / dhildenb
