[RFC PATCH 1/7] mm: Use frozen pages for page tables

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Page tables do not use the reference count.  That means we can avoid
two atomic operations (one on alloc, one on free) by allocating frozen
pages here.  This does not interfere with compaction as page tables are
non-movable allocations.

pagetable_alloc() and pagetable_free() need to move out of line to make
this work as alloc_frozen_page() and free_frozen_page() are not exported
outside the mm for now.  We'll want them out of line anyway soon.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/mm.h | 32 ++------------------------------
 mm/memory.c        | 31 +++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 30 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d16b33bacc32..ec9365375d9c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2965,37 +2965,9 @@ static inline bool pagetable_is_reserved(struct ptdesc *pt)
 	return test_bit(PT_reserved, &pt->pt_flags.f);
 }
 
-/**
- * pagetable_alloc - Allocate pagetables
- * @gfp:    GFP flags
- * @order:  desired pagetable order
- *
- * pagetable_alloc allocates memory for page tables as well as a page table
- * descriptor to describe that memory.
- *
- * Return: The ptdesc describing the allocated page tables.
- */
-static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
-{
-	struct page *page = alloc_pages_noprof(gfp | __GFP_COMP, order);
-
-	return page_ptdesc(page);
-}
+struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order);
 #define pagetable_alloc(...)	alloc_hooks(pagetable_alloc_noprof(__VA_ARGS__))
-
-/**
- * pagetable_free - Free pagetables
- * @pt:	The page table descriptor
- *
- * pagetable_free frees the memory of all page tables described by a page
- * table descriptor and the memory for the descriptor itself.
- */
-static inline void pagetable_free(struct ptdesc *pt)
-{
-	struct page *page = ptdesc_page(pt);
-
-	__free_pages(page, compound_order(page));
-}
+void pagetable_free(struct ptdesc *pt);
 
 #if defined(CONFIG_SPLIT_PTE_PTLOCKS)
 #if ALLOC_SPLIT_PTLOCKS
diff --git a/mm/memory.c b/mm/memory.c
index 74b45e258323..de9f999ffcf6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7267,6 +7267,37 @@ long copy_folio_from_user(struct folio *dst_folio,
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
+/**
+ * pagetable_alloc - Allocate pagetables
+ * @gfp:    GFP flags
+ * @order:  desired pagetable order
+ *
+ * pagetable_alloc allocates memory for page tables as well as a page table
+ * descriptor to describe that memory.
+ *
+ * Return: The ptdesc describing the allocated page tables.
+ */
+struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
+{
+	struct page *page = alloc_frozen_pages_noprof(gfp | __GFP_COMP, order);
+
+	return page_ptdesc(page);
+}
+
+/**
+ * pagetable_free - Free pagetables
+ * @pt:	The page table descriptor
+ *
+ * pagetable_free frees the memory of all page tables described by a page
+ * table descriptor and the memory for the descriptor itself.
+ */
+void pagetable_free(struct ptdesc *pt)
+{
+	struct page *page = ptdesc_page(pt);
+
+	free_frozen_pages(page, compound_order(page));
+}
+
 #if defined(CONFIG_SPLIT_PTE_PTLOCKS) && ALLOC_SPLIT_PTLOCKS
 
 static struct kmem_cache *page_ptl_cachep;
-- 
2.47.2