[RFC v2 PATCH 05/17] mm: Routines to determine max anon folio allocation order

[Ryan Roberts <ryan.roberts@arm.com>]

For variable-order anonymous folios, we want to tune the order that we
prefer to allocate based on the vma. Add the routines to manage that
heuristic.

TODO: Currently we always use the global maximum. Add per-vma logic!

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 include/linux/mm.h | 5 +++++
 mm/memory.c        | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cdb8c6031d0f..cc8d0b239116 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3674,4 +3674,9 @@ madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
 }
 #endif

+/*
+ * TODO: Should this be set per-architecture?
+ */
+#define ANON_FOLIO_ORDER_MAX	4
+
 #endif /* _LINUX_MM_H */
diff --git a/mm/memory.c b/mm/memory.c
index ca32f59acef2..d7e34a8c46aa 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3022,6 +3022,14 @@ static struct folio *try_vma_alloc_movable_folio(struct vm_area_struct *vma,
 	return vma_alloc_movable_folio(vma, vaddr, 0, zeroed);
 }

+static inline int max_anon_folio_order(struct vm_area_struct *vma)
+{
+	/*
+	 * TODO: Policy for maximum folio order should likely be per-vma.
+	 */
+	return ANON_FOLIO_ORDER_MAX;
+}
+
 /*
  * Handle write page faults for pages that can be reused in the current vma
  *
--
2.25.1