+ revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor.patch added to mm-hotfixes-unstable branch

+ revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: Revert "ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()"
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Axel Rasmussen <axelrasmussen@google.com>
Subject: Revert "ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()"
Date: Tue, 24 Feb 2026 16:24:34 -0800

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.

Link: https://lkml.kernel.org/r/20260225002434.2953895-1-axelrasmussen@google.com
Fixes: f0c92726e89f ("ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()")
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |   17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

--- a/include/linux/mm.h~revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor
+++ a/include/linux/mm.h
@@ -3514,26 +3514,21 @@ static inline bool ptlock_init(struct pt
 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)
_

Patches currently in -mm which might be from axelrasmussen@google.com are

revert-ptdesc-remove-references-to-folios-from-__pagetable_ctor-and-pagetable_dtor.patch