[PATCH] Revert "ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()"

[PATCH] Revert "ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()"

[Axel Rasmussen]

This change swapped out mod_node_page_state for lruvec_stat_add_folio.
But, these two APIs are not interchangeable: the lruvec version also
increments memcg stats, in addition to "global" pgdat stats.

So after this change, the "pagetables" memcg stat in memory.stat always
yields "0", which is a userspace visible regression.

I tried to look for a refactor where we add a variant of
lruvec_stat_mod_folio which takes a pgdat and a memcg instead of a
folio, to try to adhere to the spirit of the original patch. But at the
end of the day this just means we have to call
folio_memcg(ptdesc_folio(ptdesc)) anyway, which doesn't really
accomplish much.

This regression is visible in master as well as 6.18 stable, so CC
stable too.

Fixes: f0c92726e89f ("ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()")
Cc: stable@vger.kernel.org
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 include/linux/mm.h | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5be3d8a8f806..abb4963c1f06 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3514,26 +3514,21 @@ 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));
+	struct folio *folio = ptdesc_folio(ptdesc);
 
-	__SetPageTable(ptdesc_page(ptdesc));
-	mod_node_page_state(pgdat, NR_PAGETABLE, ptdesc_nr_pages(ptdesc));
+	__folio_set_pgtable(folio);
+	lruvec_stat_add_folio(folio, NR_PAGETABLE);
 }
 
 static inline void pagetable_dtor(struct ptdesc *ptdesc)
 {
-	pg_data_t *pgdat = NODE_DATA(memdesc_nid(ptdesc->pt_flags));
+	struct folio *folio = ptdesc_folio(ptdesc);
 
 	ptlock_free(ptdesc);
-	__ClearPageTable(ptdesc_page(ptdesc));
-	mod_node_page_state(pgdat, NR_PAGETABLE, -ptdesc_nr_pages(ptdesc));
+	__folio_clear_pgtable(folio);
+	lruvec_stat_sub_folio(folio, NR_PAGETABLE);
 }
 
 static inline void pagetable_dtor_free(struct ptdesc *ptdesc)
-- 
2.53.0.414.gf7e9f6c205-goog