[PATCH v12 mm-new 04/10] mm: thp: decouple THP allocation between swap and page fault paths

[Yafang Shao <laoar.shao@gmail.com>]

The new BPF capability enables finer-grained THP policy decisions by
introducing separate handling for swap faults versus normal page faults.

As highlighted by Barry:

  We’ve observed that swapping in large folios can lead to more
  swap thrashing for some workloads- e.g. kernel build. Consequently,
  some workloads might prefer swapping in smaller folios than those
  allocated by alloc_anon_folio().

While prtcl() could potentially be extended to leverage this new policy,
doing so would require modifications to the uAPI.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Usama Arif <usamaarif642@gmail.com>
Cc: Barry Song <21cnbao@gmail.com>
---
 include/linux/huge_mm.h | 3 ++-
 mm/huge_memory.c        | 2 +-
 mm/memory.c             | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 49050455f793..7867411b2a21 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -96,9 +96,10 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
 
 enum tva_type {
 	TVA_SMAPS,		/* Exposing "THPeligible:" in smaps. */
-	TVA_PAGEFAULT,		/* Serving a page fault. */
+	TVA_PAGEFAULT,		/* Serving a non-swap page fault. */
 	TVA_KHUGEPAGED,		/* Khugepaged collapse. */
 	TVA_FORCED_COLLAPSE,	/* Forced collapse (e.g. MADV_COLLAPSE). */
+	TVA_SWAP_PAGEFAULT,	/* serving a swap page fault. */
 };
 
 #define thp_vma_allowable_order(vma, type, order) \
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index db9a2a24d58c..0bfbb672a559 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -102,7 +102,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 					 unsigned long orders)
 {
 	const bool smaps = type == TVA_SMAPS;
-	const bool in_pf = type == TVA_PAGEFAULT;
+	const bool in_pf = (type == TVA_PAGEFAULT || type == TVA_SWAP_PAGEFAULT);
 	const bool forced_collapse = type == TVA_FORCED_COLLAPSE;
 	unsigned long supported_orders;
 	vm_flags_t vm_flags = vma->vm_flags;
diff --git a/mm/memory.c b/mm/memory.c
index 7b52068372d8..c6a766b271ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4558,7 +4558,7 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
 	 * Get a list of all the (large) orders below PMD_ORDER that are enabled
 	 * and suitable for swapping THP.
 	 */
-	orders = thp_vma_allowable_orders(vma, TVA_PAGEFAULT,
+	orders = thp_vma_allowable_orders(vma, TVA_SWAP_PAGEFAULT,
 					  BIT(PMD_ORDER) - 1);
 	orders = thp_vma_suitable_orders(vma, vmf->address, orders);
 	orders = thp_swap_suitable_orders(swp_offset(entry),
-- 
2.47.3