[RFC PATCH 2/7] mm: Account pagetable memory when allocated

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

Move the accounting from the constructor to the allocation site.
Some of the architecture code is a little complex to reason about,
but I think this is all correct (and slightly more efficient due
to having 'order' as an argument instead of having to retrieve it
from struct page again).

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/mm.h | 11 -----------
 mm/memory.c        | 11 ++++++++++-
 2 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ec9365375d9c..ade37df5ea2b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3044,26 +3044,15 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
 static inline void ptlock_free(struct ptdesc *ptdesc) {}
 #endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */
 
-static inline unsigned long ptdesc_nr_pages(const struct ptdesc *ptdesc)
-{
-	return compound_nr(ptdesc_page(ptdesc));
-}
-
 static inline void __pagetable_ctor(struct ptdesc *ptdesc)
 {
-	pg_data_t *pgdat = NODE_DATA(memdesc_nid(ptdesc->pt_flags));
-
 	__SetPageTable(ptdesc_page(ptdesc));
-	mod_node_page_state(pgdat, NR_PAGETABLE, ptdesc_nr_pages(ptdesc));
 }
 
 static inline void pagetable_dtor(struct ptdesc *ptdesc)
 {
-	pg_data_t *pgdat = NODE_DATA(memdesc_nid(ptdesc->pt_flags));
-
 	ptlock_free(ptdesc);
 	__ClearPageTable(ptdesc_page(ptdesc));
-	mod_node_page_state(pgdat, NR_PAGETABLE, -ptdesc_nr_pages(ptdesc));
 }
 
 static inline void pagetable_dtor_free(struct ptdesc *ptdesc)
diff --git a/mm/memory.c b/mm/memory.c
index de9f999ffcf6..033fc4e29232 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7280,7 +7280,13 @@ long copy_folio_from_user(struct folio *dst_folio,
 struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
 {
 	struct page *page = alloc_frozen_pages_noprof(gfp | __GFP_COMP, order);
+	pg_data_t *pgdat;
 
+	if (!page)
+		return NULL;
+
+	pgdat = NODE_DATA(page_to_nid(page));
+	mod_node_page_state(pgdat, NR_PAGETABLE, 1 << order);
 	return page_ptdesc(page);
 }
 
@@ -7293,9 +7299,12 @@ struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
  */
 void pagetable_free(struct ptdesc *pt)
 {
+	pg_data_t *pgdat = NODE_DATA(memdesc_nid(pt->pt_flags));
 	struct page *page = ptdesc_page(pt);
+	unsigned int order = compound_order(page);
 
-	free_frozen_pages(page, compound_order(page));
+	mod_node_page_state(pgdat, NR_PAGETABLE, -(1L << order));
+	free_frozen_pages(page, order);
 }
 
 #if defined(CONFIG_SPLIT_PTE_PTLOCKS) && ALLOC_SPLIT_PTLOCKS
-- 
2.47.2