mm: introduce memdesc_flags_t

Patch series "Add and use memdesc_flags_t".

At some point struct page will be separated from struct slab and struct
folio.  This is a step towards that by introducing a type for the 'flags'
word of all three structures.  This gives us a certain amount of type
safety by establishing that some of these unsigned longs are different
from other unsigned longs in that they contain things like node ID,
section number and zone number in the upper bits.  That lets us have
functions that can be easily called by anyone who has a slab, folio or
page (but not easily by anyone else) to get the node or zone.

There's going to be some unusual merge problems with this as some odd bits
of the kernel decide they want to print out the flags value or something
similar by writing page->flags and now they'll need to write page->flags.f
instead.  That's most of the churn here.  Maybe we should be removing
these things from the debug output?


This patch (of 11):

Wrap the unsigned long flags in a typedef.  In upcoming patches, this will
provide a strong hint that you can't just pass a random unsigned long to
functions which take this as an argument.

[willy@infradead.org: s/flags/flags.f/ in several architectures]
  Link: https://lkml.kernel.org/r/aKMgPRLD-WnkPxYm@casper.infradead.org
[nicola.vetrini@gmail.com: mips: fix compilation error]
  Link: https://lore.kernel.org/lkml/CA+G9fYvkpmqGr6wjBNHY=dRp71PLCoi2341JxOudi60yqaeUdg@mail.gmail.com/
  Link: https://lkml.kernel.org/r/20250825214245.1838158-1-nicola.vetrini@gmail.com
Link: https://lkml.kernel.org/r/20250805172307.1302730-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20250805172307.1302730-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

7 files changed, 55 insertions, 50 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b61e2d4858cf..da562f23f50c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1024,7 +1024,7 @@ static inline unsigned int compound_order(struct page *page)
 {
 	struct folio *folio = (struct folio *)page;
 
-	if (!test_bit(PG_head, &folio->flags))
+	if (!test_bit(PG_head, &folio->flags.f))
 		return 0;
 	return folio_large_order(folio);
 }
@@ -1554,7 +1554,7 @@ static inline bool is_nommu_shared_mapping(vm_flags_t flags)
  */
 static inline int page_zone_id(struct page *page)
 {
-	return (page->flags >> ZONEID_PGSHIFT) & ZONEID_MASK;
+	return (page->flags.f >> ZONEID_PGSHIFT) & ZONEID_MASK;
 }
 
 #ifdef NODE_NOT_IN_PAGE_FLAGS
@@ -1562,7 +1562,7 @@ int page_to_nid(const struct page *page);
 #else
 static inline int page_to_nid(const struct page *page)
 {
-	return (PF_POISONED_CHECK(page)->flags >> NODES_PGSHIFT) & NODES_MASK;
+	return (PF_POISONED_CHECK(page)->flags.f >> NODES_PGSHIFT) & NODES_MASK;
 }
 #endif
 
@@ -1637,14 +1637,14 @@ static inline void page_cpupid_reset_last(struct page *page)
 #else
 static inline int folio_last_cpupid(struct folio *folio)
 {
-	return (folio->flags >> LAST_CPUPID_PGSHIFT) & LAST_CPUPID_MASK;
+	return (folio->flags.f >> LAST_CPUPID_PGSHIFT) & LAST_CPUPID_MASK;
 }
 
 int folio_xchg_last_cpupid(struct folio *folio, int cpupid);
 
 static inline void page_cpupid_reset_last(struct page *page)
 {
-	page->flags |= LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT;
+	page->flags.f |= LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT;
 }
 #endif /* LAST_CPUPID_NOT_IN_PAGE_FLAGS */
 
@@ -1740,7 +1740,7 @@ static inline u8 page_kasan_tag(const struct page *page)
 	u8 tag = KASAN_TAG_KERNEL;
 
 	if (kasan_enabled()) {
-		tag = (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
+		tag = (page->flags.f >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
 		tag ^= 0xff;
 	}
 
@@ -1755,12 +1755,12 @@ static inline void page_kasan_tag_set(struct page *page, u8 tag)
 		return;
 
 	tag ^= 0xff;
-	old_flags = READ_ONCE(page->flags);
+	old_flags = READ_ONCE(page->flags.f);
 	do {
 		flags = old_flags;
 		flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
 		flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
-	} while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
+	} while (unlikely(!try_cmpxchg(&page->flags.f, &old_flags, flags)));
 }
 
 static inline void page_kasan_tag_reset(struct page *page)
@@ -1804,13 +1804,13 @@ static inline pg_data_t *folio_pgdat(const struct folio *folio)
 #ifdef SECTION_IN_PAGE_FLAGS
 static inline void set_page_section(struct page *page, unsigned long section)
 {
-	page->flags &= ~(SECTIONS_MASK << SECTIONS_PGSHIFT);
-	page->flags |= (section & SECTIONS_MASK) << SECTIONS_PGSHIFT;
+	page->flags.f &= ~(SECTIONS_MASK << SECTIONS_PGSHIFT);
+	page->flags.f |= (section & SECTIONS_MASK) << SECTIONS_PGSHIFT;
 }
 
 static inline unsigned long page_to_section(const struct page *page)
 {
-	return (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
+	return (page->flags.f >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
 }
 #endif
 
@@ -2015,14 +2015,14 @@ static inline bool folio_is_longterm_pinnable(struct folio *folio)
 
 static inline void set_page_zone(struct page *page, enum zone_type zone)
 {
-	page->flags &= ~(ZONES_MASK << ZONES_PGSHIFT);
-	page->flags |= (zone & ZONES_MASK) << ZONES_PGSHIFT;
+	page->flags.f &= ~(ZONES_MASK << ZONES_PGSHIFT);
+	page->flags.f |= (zone & ZONES_MASK) << ZONES_PGSHIFT;
 }
 
 static inline void set_page_node(struct page *page, unsigned long node)
 {
-	page->flags &= ~(NODES_MASK << NODES_PGSHIFT);
-	page->flags |= (node & NODES_MASK) << NODES_PGSHIFT;
+	page->flags.f &= ~(NODES_MASK << NODES_PGSHIFT);
+	page->flags.f |= (node & NODES_MASK) << NODES_PGSHIFT;
 }
 
 static inline void set_page_links(struct page *page, enum zone_type zone,
@@ -2064,7 +2064,7 @@ static inline long compound_nr(struct page *page)
 {
 	struct folio *folio = (struct folio *)page;
 
-	if (!test_bit(PG_head, &folio->flags))
+	if (!test_bit(PG_head, &folio->flags.f))
 		return 1;
 	return folio_large_nr_pages(folio);
 }
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 89b518ff097e..150302b4a905 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -143,7 +143,7 @@ static inline int lru_tier_from_refs(int refs, bool workingset)
 
 static inline int folio_lru_refs(struct folio *folio)
 {
-	unsigned long flags = READ_ONCE(folio->flags);
+	unsigned long flags = READ_ONCE(folio->flags.f);
 
 	if (!(flags & BIT(PG_referenced)))
 		return 0;
@@ -156,7 +156,7 @@ static inline int folio_lru_refs(struct folio *folio)
 
 static inline int folio_lru_gen(struct folio *folio)
 {
-	unsigned long flags = READ_ONCE(folio->flags);
+	unsigned long flags = READ_ONCE(folio->flags.f);
 
 	return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
 }
@@ -268,7 +268,7 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	gen = lru_gen_from_seq(seq);
 	flags = (gen + 1UL) << LRU_GEN_PGOFF;
 	/* see the comment on MIN_NR_GENS about PG_active */
-	set_mask_bits(&folio->flags, LRU_GEN_MASK | BIT(PG_active), flags);
+	set_mask_bits(&folio->flags.f, LRU_GEN_MASK | BIT(PG_active), flags);
 
 	lru_gen_update_size(lruvec, folio, -1, gen);
 	/* for folio_rotate_reclaimable() */
@@ -293,7 +293,7 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 
 	/* for folio_migrate_flags() */
 	flags = !reclaiming && lru_gen_is_active(lruvec, gen) ? BIT(PG_active) : 0;
-	flags = set_mask_bits(&folio->flags, LRU_GEN_MASK, flags);
+	flags = set_mask_bits(&folio->flags.f, LRU_GEN_MASK, flags);
 	gen = ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
 
 	lru_gen_update_size(lruvec, folio, gen, -1);
@@ -304,9 +304,9 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 
 static inline void folio_migrate_refs(struct folio *new, struct folio *old)
 {
-	unsigned long refs = READ_ONCE(old->flags) & LRU_REFS_MASK;
+	unsigned long refs = READ_ONCE(old->flags.f) & LRU_REFS_MASK;
 
-	set_mask_bits(&new->flags, LRU_REFS_MASK, refs);
+	set_mask_bits(&new->flags.f, LRU_REFS_MASK, refs);
 }
 #else /* !CONFIG_LRU_GEN */
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index d247da2fdb52..d934a3a5b443 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -34,6 +34,10 @@ struct address_space;
 struct futex_private_hash;
 struct mem_cgroup;
 
+typedef struct {
+	unsigned long f;
+} memdesc_flags_t;
+
 /*
  * Each physical page in the system has a struct page associated with
  * it to keep track of whatever it is we are using the page for at the
@@ -72,7 +76,7 @@ struct mem_cgroup;
 #endif
 
 struct page {
-	unsigned long flags;		/* Atomic flags, some possibly
+	memdesc_flags_t flags;		/* Atomic flags, some possibly
 					 * updated asynchronously */
 	/*
 	 * Five words (20/40 bytes) are available in this union.
@@ -383,7 +387,7 @@ struct folio {
 	union {
 		struct {
 	/* public: */
-			unsigned long flags;
+			memdesc_flags_t flags;
 			union {
 				struct list_head lru;
 	/* private: avoid cluttering the output */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9d3ea9085556..990560cd99ee 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1186,7 +1186,7 @@ static inline bool zone_is_empty(struct zone *zone)
 static inline enum zone_type page_zonenum(const struct page *page)
 {
 	ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT);
-	return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK;
+	return (page->flags.f >> ZONES_PGSHIFT) & ZONES_MASK;
 }
 
 static inline enum zone_type folio_zonenum(const struct folio *folio)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 8d3fa3a91ce4..d53a86e68c89 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -217,7 +217,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page
 	 * cold cacheline in some cases.
 	 */
 	if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) &&
-	    test_bit(PG_head, &page->flags)) {
+	    test_bit(PG_head, &page->flags.f)) {
 		/*
 		 * We can safely access the field of the @page[1] with PG_head
 		 * because the @page is a compound page composed with at least
@@ -325,14 +325,14 @@ static __always_inline int PageTail(const struct page *page)
 
 static __always_inline int PageCompound(const struct page *page)
 {
-	return test_bit(PG_head, &page->flags) ||
+	return test_bit(PG_head, &page->flags.f) ||
 	       READ_ONCE(page->compound_head) & 1;
 }
 
 #define	PAGE_POISON_PATTERN	-1l
 static inline int PagePoisoned(const struct page *page)
 {
-	return READ_ONCE(page->flags) == PAGE_POISON_PATTERN;
+	return READ_ONCE(page->flags.f) == PAGE_POISON_PATTERN;
 }
 
 #ifdef CONFIG_DEBUG_VM
@@ -349,8 +349,8 @@ static const unsigned long *const_folio_flags(const struct folio *folio,
 	const struct page *page = &folio->page;
 
 	VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);
-	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);
-	return &page[n].flags;
+	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);
+	return &page[n].flags.f;
 }
 
 static unsigned long *folio_flags(struct folio *folio, unsigned n)
@@ -358,8 +358,8 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
 	struct page *page = &folio->page;
 
 	VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);
-	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);
-	return &page[n].flags;
+	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);
+	return &page[n].flags.f;
 }
 
 /*
@@ -449,37 +449,37 @@ FOLIO_CLEAR_FLAG(name, page)
 #define TESTPAGEFLAG(uname, lname, policy)				\
 FOLIO_TEST_FLAG(lname, FOLIO_##policy)					\
 static __always_inline int Page##uname(const struct page *page)		\
-{ return test_bit(PG_##lname, &policy(page, 0)->flags); }
+{ return test_bit(PG_##lname, &policy(page, 0)->flags.f); }
 
 #define SETPAGEFLAG(uname, lname, policy)				\
 FOLIO_SET_FLAG(lname, FOLIO_##policy)					\
 static __always_inline void SetPage##uname(struct page *page)		\
-{ set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ set_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define CLEARPAGEFLAG(uname, lname, policy)				\
 FOLIO_CLEAR_FLAG(lname, FOLIO_##policy)					\
 static __always_inline void ClearPage##uname(struct page *page)		\
-{ clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ clear_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define __SETPAGEFLAG(uname, lname, policy)				\
 __FOLIO_SET_FLAG(lname, FOLIO_##policy)					\
 static __always_inline void __SetPage##uname(struct page *page)		\
-{ __set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ __set_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define __CLEARPAGEFLAG(uname, lname, policy)				\
 __FOLIO_CLEAR_FLAG(lname, FOLIO_##policy)				\
 static __always_inline void __ClearPage##uname(struct page *page)	\
-{ __clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ __clear_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define TESTSETFLAG(uname, lname, policy)				\
 FOLIO_TEST_SET_FLAG(lname, FOLIO_##policy)				\
 static __always_inline int TestSetPage##uname(struct page *page)	\
-{ return test_and_set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ return test_and_set_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define TESTCLEARFLAG(uname, lname, policy)				\
 FOLIO_TEST_CLEAR_FLAG(lname, FOLIO_##policy)				\
 static __always_inline int TestClearPage##uname(struct page *page)	\
-{ return test_and_clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ return test_and_clear_bit(PG_##lname, &policy(page, 1)->flags.f); }
 
 #define PAGEFLAG(uname, lname, policy)					\
 	TESTPAGEFLAG(uname, lname, policy)				\
@@ -846,7 +846,7 @@ static __always_inline bool folio_test_head(const struct folio *folio)
 static __always_inline int PageHead(const struct page *page)
 {
 	PF_POISONED_CHECK(page);
-	return test_bit(PG_head, &page->flags) && !page_is_fake_head(page);
+	return test_bit(PG_head, &page->flags.f) && !page_is_fake_head(page);
 }
 
 __SETPAGEFLAG(Head, head, PF_ANY)
@@ -1170,28 +1170,28 @@ static __always_inline int PageAnonExclusive(const struct page *page)
 	 */
 	if (PageHuge(page))
 		page = compound_head(page);
-	return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);
+	return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags.f);
 }
 
 static __always_inline void SetPageAnonExclusive(struct page *page)
 {
 	VM_BUG_ON_PGFLAGS(!PageAnonNotKsm(page), page);
 	VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
-	set_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);
+	set_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags.f);
 }
 
 static __always_inline void ClearPageAnonExclusive(struct page *page)
 {
 	VM_BUG_ON_PGFLAGS(!PageAnonNotKsm(page), page);
 	VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
-	clear_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);
+	clear_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags.f);
 }
 
 static __always_inline void __ClearPageAnonExclusive(struct page *page)
 {
 	VM_BUG_ON_PGFLAGS(!PageAnon(page), page);
 	VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
-	__clear_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);
+	__clear_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags.f);
 }
 
 #ifdef CONFIG_MMU
@@ -1241,7 +1241,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
  */
 static inline int folio_has_private(const struct folio *folio)
 {
-	return !!(folio->flags & PAGE_FLAGS_PRIVATE);
+	return !!(folio->flags.f & PAGE_FLAGS_PRIVATE);
 }
 
 #undef PF_ANY
diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 8a7f4f802c57..38a82d65e58e 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -107,7 +107,8 @@ static inline bool get_page_tag_ref(struct page *page, union codetag_ref *ref,
 	if (static_key_enabled(&mem_profiling_compressed)) {
 		pgalloc_tag_idx idx;
 
-		idx = (page->flags >> alloc_tag_ref_offs) & alloc_tag_ref_mask;
+		idx = (page->flags.f >> alloc_tag_ref_offs) &
+			alloc_tag_ref_mask;
 		idx_to_ref(idx, ref);
 		handle->page = page;
 	} else {
@@ -149,11 +150,11 @@ static inline void update_page_tag_ref(union pgtag_ref_handle handle, union code
 		idx = (unsigned long)ref_to_idx(ref);
 		idx = (idx & alloc_tag_ref_mask) << alloc_tag_ref_offs;
 		do {
-			old_flags = READ_ONCE(page->flags);
+			old_flags = READ_ONCE(page->flags.f);
 			flags = old_flags;
 			flags &= ~(alloc_tag_ref_mask << alloc_tag_ref_offs);
 			flags |= idx;
-		} while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
+		} while (unlikely(!try_cmpxchg(&page->flags.f, &old_flags, flags)));
 	} else {
 		if (WARN_ON(!handle.ref || !ref))
 			return;
diff --git a/include/trace/events/page_ref.h b/include/trace/events/page_ref.h
index fe33a255b7d0..ea6b5c4baf3d 100644
--- a/include/trace/events/page_ref.h
+++ b/include/trace/events/page_ref.h
@@ -28,7 +28,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
 
 	TP_fast_assign(
 		__entry->pfn = page_to_pfn(page);
-		__entry->flags = page->flags;
+		__entry->flags = page->flags.f;
 		__entry->count = page_ref_count(page);
 		__entry->mapcount = atomic_read(&page->_mapcount);
 		__entry->mapping = page->mapping;
@@ -77,7 +77,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
 
 	TP_fast_assign(
 		__entry->pfn = page_to_pfn(page);
-		__entry->flags = page->flags;
+		__entry->flags = page->flags.f;
 		__entry->count = page_ref_count(page);
 		__entry->mapcount = atomic_read(&page->_mapcount);
 		__entry->mapping = page->mapping;