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>

1 files changed, 20 insertions, 20 deletions

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