[RFC v2 PATCH 03/17] mm: Introduce try_vma_alloc_movable_folio()

Ryan Roberts
2023-04-14T13:03:29Z

Opportunistically attempt to allocate high-order folios in highmem,
optionally zeroed. Retry with lower orders all the way to order-0, until
success. Although, of note, order-1 allocations are skipped since a
large folio must be at least order-2 to work with the THP machinery. The
user must check what they got with folio_order().

This will be used to oportunistically allocate large folios for
anonymous memory with a sensible fallback under memory pressure.

For attempts to allocate non-0 orders, we set __GFP_NORETRY to prevent
high latency due to reclaim, instead preferring to just try for a lower
order. The same approach is used by the readahead code when allocating
large folios.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
mm/memory.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 9d5e8be49f3b..ca32f59acef2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2989,6 +2989,39 @@ static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
return 0;
}

+static inline struct folio *vma_alloc_movable_folio(struct vm_area_struct *vma,
+ unsigned long vaddr, int order, bool zeroed)
+{
+ gfp_t gfp = order > 0 ? __GFP_NORETRY | __GFP_NOWARN : 0;
+
+ if (zeroed)
+ return vma_alloc_zeroed_movable_folio(vma, vaddr, gfp, order);
+ else
+ return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp, order, vma,
+ vaddr, false);
+}
+
+/*
+ * Opportunistically attempt to allocate high-order folios, retrying with lower
+ * orders all the way to order-0, until success. order-1 allocations are skipped
+ * since a folio must be at least order-2 to work with the THP machinery. The
+ * user must check what they got with folio_order(). vaddr can be any virtual
+ * address that will be mapped by the allocated folio.
+ */
+static struct folio *try_vma_alloc_movable_folio(struct vm_area_struct *vma,
+ unsigned long vaddr, int order, bool zeroed)
+{
+ struct folio *folio;
+
+ for (; order > 1; order--) {
+ folio = vma_alloc_movable_folio(vma, vaddr, order, zeroed);
+ if (folio)
+ return folio;
+ }
+
+ return vma_alloc_movable_folio(vma, vaddr, 0, zeroed);
+}
+
/*
* Handle write page faults for pages that can be reused in the current vma
*
--
2.25.1