The quilt patch titled
Subject: mm: let _folio_nr_pages overlay memcg_data in first tail page
has been removed from the -mm tree. Its filename was
mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: let _folio_nr_pages overlay memcg_data in first tail page
Date: Mon, 3 Mar 2025 17:29:56 +0100
Let's free up some more of the "unconditionally available on 64BIT" space
in order-1 folios by letting _folio_nr_pages overlay memcg_data in the
first tail page (second folio page). Consequently, we have the
optimization now whenever we have CONFIG_MEMCG, independent of 64BIT.
We have to make sure that page->memcg on tail pages does not return
"surprises". page_memcg_check() already properly refuses PageTail().
Let's do that earlier in print_page_owner_memcg() to avoid printing wrong
"Slab cache page" information. No other code should touch that field on
tail pages of compound pages.
Reset the "_nr_pages" to 0 when splitting folios, or when freeing them
back to the buddy (to avoid false page->memcg_data "bad page" reports).
Note that in __split_huge_page(), folio_nr_pages() would stop working
already as soon as we start messing with the subpages.
Most kernel configs should have at least CONFIG_MEMCG enabled, even if
disabled at runtime. 64byte "struct memmap" is what we usually have on
64BIT.
While at it, rename "_folio_nr_pages" to "_nr_pages".
Hopefully memdescs / dynamically allocating "strut folio" in the future
will further clean this up, e.g., making _nr_pages available in all
configs and maybe even in small folios. Doing that should be fairly easy
on top of this change.
[david@xxxxxxxxxx: make "make htmldoc" happy]
Link: https://lkml.kernel.org/r/a97f8a91-ec41-4796-81e3-7c9e0e491ba4@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20250303163014.1128035-4-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirks^H^Hski <luto@xxxxxxxxxx>
Cc: Borislav Betkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Matthew Wilcow (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Koutn <mkoutny@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: tejun heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 4 ++--
include/linux/mm_types.h | 32 ++++++++++++++++++++++++--------
mm/huge_memory.c | 8 ++++++++
mm/internal.h | 4 ++--
mm/page_alloc.c | 6 +++++-
mm/page_owner.c | 2 +-
6 files changed, 42 insertions(+), 14 deletions(-)
--- a/include/linux/mm.h~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/include/linux/mm.h
@@ -1199,10 +1199,10 @@ static inline unsigned int folio_large_o
return folio->_flags_1 & 0xff;
}
-#ifdef CONFIG_64BIT
+#ifdef NR_PAGES_IN_LARGE_FOLIO
static inline long folio_large_nr_pages(const struct folio *folio)
{
- return folio->_folio_nr_pages;
+ return folio->_nr_pages;
}
#else
static inline long folio_large_nr_pages(const struct folio *folio)
--- a/include/linux/mm_types.h~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/include/linux/mm_types.h
@@ -287,6 +287,11 @@ typedef struct {
unsigned long val;
} swp_entry_t;
+#if defined(CONFIG_MEMCG) || defined(CONFIG_SLAB_OBJ_EXT)
+/* We have some extra room after the refcount in tail pages. */
+#define NR_PAGES_IN_LARGE_FOLIO
+#endif
+
/**
* struct folio - Represents a contiguous set of bytes.
* @flags: Identical to the page flags.
@@ -312,7 +317,7 @@ typedef struct {
* @_large_mapcount: Do not use directly, call folio_mapcount().
* @_nr_pages_mapped: Do not use outside of rmap and debug code.
* @_pincount: Do not use directly, call folio_maybe_dma_pinned().
- * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
+ * @_nr_pages: Do not use directly, call folio_nr_pages().
* @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
* @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
* @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
@@ -376,14 +381,23 @@ struct folio {
struct {
unsigned long _flags_1;
unsigned long _head_1;
+ union {
+ struct {
/* public: */
- atomic_t _large_mapcount;
- atomic_t _entire_mapcount;
- atomic_t _nr_pages_mapped;
- atomic_t _pincount;
-#ifdef CONFIG_64BIT
- unsigned int _folio_nr_pages;
-#endif
+ atomic_t _large_mapcount;
+ atomic_t _entire_mapcount;
+ atomic_t _nr_pages_mapped;
+ atomic_t _pincount;
+ /* private: the union with struct page is transitional */
+ };
+ unsigned long _usable_1[4];
+ };
+ atomic_t _mapcount_1;
+ atomic_t _refcount_1;
+ /* public: */
+#ifdef NR_PAGES_IN_LARGE_FOLIO
+ unsigned int _nr_pages;
+#endif /* NR_PAGES_IN_LARGE_FOLIO */
/* private: the union with struct page is transitional */
};
struct page __page_1;
@@ -435,6 +449,8 @@ FOLIO_MATCH(_last_cpupid, _last_cpupid);
offsetof(struct page, pg) + sizeof(struct page))
FOLIO_MATCH(flags, _flags_1);
FOLIO_MATCH(compound_head, _head_1);
+FOLIO_MATCH(_mapcount, _mapcount_1);
+FOLIO_MATCH(_refcount, _refcount_1);
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl) \
static_assert(offsetof(struct folio, fl) == \
--- a/mm/huge_memory.c~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/mm/huge_memory.c
@@ -3399,6 +3399,14 @@ static void __split_huge_page(struct pag
int order = folio_order(folio);
unsigned int nr = 1 << order;
+ /*
+ * Reset any memcg data overlay in the tail pages. folio_nr_pages()
+ * is unreliable after this point.
+ */
+#ifdef NR_PAGES_IN_LARGE_FOLIO
+ folio->_nr_pages = 0;
+#endif
+
/* complete memcg works before add pages to LRU */
split_page_memcg(head, order, new_order);
--- a/mm/internal.h~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/mm/internal.h
@@ -725,8 +725,8 @@ static inline void folio_set_order(struc
return;
folio->_flags_1 = (folio->_flags_1 & ~0xffUL) | order;
-#ifdef CONFIG_64BIT
- folio->_folio_nr_pages = 1U << order;
+#ifdef NR_PAGES_IN_LARGE_FOLIO
+ folio->_nr_pages = 1U << order;
#endif
}
--- a/mm/page_alloc.c~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/mm/page_alloc.c
@@ -1174,8 +1174,12 @@ __always_inline bool free_pages_prepare(
if (unlikely(order)) {
int i;
- if (compound)
+ if (compound) {
page[1].flags &= ~PAGE_FLAGS_SECOND;
+#ifdef NR_PAGES_IN_LARGE_FOLIO
+ folio->_nr_pages = 0;
+#endif
+ }
for (i = 1; i < (1 << order); i++) {
if (compound)
bad += free_tail_page_prepare(page, page + i);
--- a/mm/page_owner.c~mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page
+++ a/mm/page_owner.c
@@ -507,7 +507,7 @@ static inline int print_page_owner_memcg
rcu_read_lock();
memcg_data = READ_ONCE(page->memcg_data);
- if (!memcg_data)
+ if (!memcg_data || PageTail(page))
goto out_unlock;
if (memcg_data & MEMCG_DATA_OBJEXTS)
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
