[PATCH] mm: Make some folio and page function arguments const and use bool

From: David Howells
Date: Thu Nov 10 2022 - 12:30:36 EST

Mark the folio* argument to some of the folio accessor functions as a const
pointer and similarly make some page* arguments to some page functions
const.

Also switch the return values to bool rather than int where the test inside
produces a bool.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

include/linux/mm.h | 20 ++++-----
include/linux/page-flags.h | 99 ++++++++++++++++++++++++--------------------
mm/hugetlb.c | 8 ++--
mm/page_alloc.c | 4 +-
4 files changed, 70 insertions(+), 61 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7a7a287818ad..a069f6f70aed 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -711,7 +711,7 @@ int vma_is_stack_for_current(struct vm_area_struct *vma);
struct mmu_gather;
struct inode;

-static inline unsigned int compound_order(struct page *page)
+static inline unsigned int compound_order(const struct page *page)
{
if (!PageHead(page))
return 0;
@@ -727,7 +727,7 @@ static inline unsigned int compound_order(struct page *page)
*
* Return: The order of the folio.
*/
-static inline unsigned int folio_order(struct folio *folio)
+static inline unsigned int folio_order(const struct folio *folio)
{
if (!folio_test_large(folio))
return 0;
@@ -945,7 +945,7 @@ static inline void set_compound_order(struct page *page, unsigned int order)
}

/* Returns the number of pages in this potentially compound page. */
-static inline unsigned long compound_nr(struct page *page)
+static inline unsigned long compound_nr(const struct page *page)
{
if (!PageHead(page))
return 1;
@@ -1519,7 +1519,7 @@ static inline unsigned long page_to_section(const struct page *page)
*
* Return: The Page Frame Number of the first page in the folio.
*/
-static inline unsigned long folio_pfn(struct folio *folio)
+static inline unsigned long folio_pfn(const struct folio *folio)
{
return page_to_pfn(&folio->page);
}
@@ -1600,7 +1600,7 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,

/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin pages */
#ifdef CONFIG_MIGRATION
-static inline bool is_longterm_pinnable_page(struct page *page)
+static inline bool is_longterm_pinnable_page(const struct page *page)
{
#ifdef CONFIG_CMA
int mt = get_pageblock_migratetype(page);
@@ -1620,13 +1620,13 @@ static inline bool is_longterm_pinnable_page(struct page *page)
return !is_zone_movable_page(page);
}
#else
-static inline bool is_longterm_pinnable_page(struct page *page)
+static inline bool is_longterm_pinnable_page(const struct page *page)
{
return true;
}
#endif

-static inline bool folio_is_longterm_pinnable(struct folio *folio)
+static inline bool folio_is_longterm_pinnable(const struct folio *folio)
{
return is_longterm_pinnable_page(&folio->page);
}
@@ -1659,7 +1659,7 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
*
* Return: A positive power of two.
*/
-static inline long folio_nr_pages(struct folio *folio)
+static inline long folio_nr_pages(const struct folio *folio)
{
if (!folio_test_large(folio))
return 1;
@@ -1701,7 +1701,7 @@ static inline struct folio *folio_next(struct folio *folio)
* it from being split. It is not necessary for the folio to be locked.
* Return: The base-2 logarithm of the size of this folio.
*/
-static inline unsigned int folio_shift(struct folio *folio)
+static inline unsigned int folio_shift(const struct folio *folio)
{
return PAGE_SHIFT + folio_order(folio);
}
@@ -1714,7 +1714,7 @@ static inline unsigned int folio_shift(struct folio *folio)
* it from being split. It is not necessary for the folio to be locked.
* Return: The number of bytes in this folio.
*/
-static inline size_t folio_size(struct folio *folio)
+static inline size_t folio_size(const struct folio *folio)
{
return PAGE_SIZE << folio_order(folio);
}
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0b0ae5084e60..ee6604fcc1d1 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -243,7 +243,7 @@ static inline const struct page *page_fixed_fake_head(const struct page *page)
}
#endif

-static __always_inline int page_is_fake_head(struct page *page)
+static __always_inline bool page_is_fake_head(const struct page *page)
{
return page_fixed_fake_head(page) != page;
}
@@ -287,19 +287,19 @@ static inline unsigned long _compound_head(const struct page *page)
*/
#define folio_page(folio, n) nth_page(&(folio)->page, n)

-static __always_inline int PageTail(struct page *page)
+static __always_inline bool PageTail(const struct page *page)
{
return READ_ONCE(page->compound_head) & 1 || page_is_fake_head(page);
}

-static __always_inline int PageCompound(struct page *page)
+static __always_inline bool PageCompound(const struct page *page)
{
return test_bit(PG_head, &page->flags) ||
READ_ONCE(page->compound_head) & 1;
}

#define PAGE_POISON_PATTERN -1l
-static inline int PagePoisoned(const struct page *page)
+static inline bool PagePoisoned(const struct page *page)
{
return READ_ONCE(page->flags) == PAGE_POISON_PATTERN;
}
@@ -312,6 +312,15 @@ static inline void page_init_poison(struct page *page, size_t size)
}
#endif

+static const unsigned long *const_folio_flags(const struct folio *folio, unsigned n)
+{
+ const struct page *page = &folio->page;
+
+ VM_BUG_ON_PGFLAGS(PageTail(page), page);
+ VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);
+ return &page[n].flags;
+}
+
static unsigned long *folio_flags(struct folio *folio, unsigned n)
{
struct page *page = &folio->page;
@@ -377,9 +386,9 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
* Macros to create function definitions for page flags
*/
#define TESTPAGEFLAG(uname, lname, policy) \
-static __always_inline bool folio_test_##lname(struct folio *folio) \
-{ return test_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
-static __always_inline int Page##uname(struct page *page) \
+static __always_inline bool folio_test_##lname(const struct folio *folio) \
+{ return test_bit(PG_##lname, const_folio_flags(folio, FOLIO_##policy)); } \
+static __always_inline bool Page##uname(const struct page *page) \
{ return test_bit(PG_##lname, &policy(page, 0)->flags); }

#define SETPAGEFLAG(uname, lname, policy) \
@@ -414,14 +423,14 @@ static __always_inline void __ClearPage##uname(struct page *page) \
static __always_inline \
bool folio_test_set_##lname(struct folio *folio) \
{ return test_and_set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
-static __always_inline int TestSetPage##uname(struct page *page) \
+static __always_inline bool TestSetPage##uname(struct page *page) \
{ return test_and_set_bit(PG_##lname, &policy(page, 1)->flags); }

#define TESTCLEARFLAG(uname, lname, policy) \
static __always_inline \
bool folio_test_clear_##lname(struct folio *folio) \
{ return test_and_clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \
-static __always_inline int TestClearPage##uname(struct page *page) \
+static __always_inline bool TestClearPage##uname(struct page *page) \
{ return test_and_clear_bit(PG_##lname, &policy(page, 1)->flags); }

#define PAGEFLAG(uname, lname, policy) \
@@ -440,7 +449,7 @@ static __always_inline int TestClearPage##uname(struct page *page) \

#define TESTPAGEFLAG_FALSE(uname, lname) \
static inline bool folio_test_##lname(const struct folio *folio) { return false; } \
-static inline int Page##uname(const struct page *page) { return 0; }
+static inline bool Page##uname(const struct page *page) { return false; }

#define SETPAGEFLAG_NOOP(uname, lname) \
static inline void folio_set_##lname(struct folio *folio) { } \
@@ -456,13 +465,13 @@ static inline void __ClearPage##uname(struct page *page) { }

#define TESTSETFLAG_FALSE(uname, lname) \
static inline bool folio_test_set_##lname(struct folio *folio) \
-{ return 0; } \
-static inline int TestSetPage##uname(struct page *page) { return 0; }
+{ return false; } \
+static inline bool TestSetPage##uname(struct page *page) { return false; }

#define TESTCLEARFLAG_FALSE(uname, lname) \
static inline bool folio_test_clear_##lname(struct folio *folio) \
-{ return 0; } \
-static inline int TestClearPage##uname(struct page *page) { return 0; }
+{ return false; } \
+static inline bool TestClearPage##uname(struct page *page) { return false; }

#define PAGEFLAG_FALSE(uname, lname) TESTPAGEFLAG_FALSE(uname, lname) \
SETPAGEFLAG_NOOP(uname, lname) CLEARPAGEFLAG_NOOP(uname, lname)
@@ -538,13 +547,13 @@ PAGEFLAG_FALSE(HighMem, highmem)
#endif

#ifdef CONFIG_SWAP
-static __always_inline bool folio_test_swapcache(struct folio *folio)
+static __always_inline bool folio_test_swapcache(const struct folio *folio)
{
return folio_test_swapbacked(folio) &&
- test_bit(PG_swapcache, folio_flags(folio, 0));
+ test_bit(PG_swapcache, const_folio_flags(folio, 0));
}

-static __always_inline bool PageSwapCache(struct page *page)
+static __always_inline bool PageSwapCache(const struct page *page)
{
return folio_test_swapcache(page_folio(page));
}
@@ -643,22 +652,22 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
*/
#define PAGE_MAPPING_DAX_COW 0x1

-static __always_inline bool folio_mapping_flags(struct folio *folio)
+static __always_inline bool folio_mapping_flags(const struct folio *folio)
{
return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) != 0;
}

-static __always_inline int PageMappingFlags(struct page *page)
+static __always_inline bool PageMappingFlags(const struct page *page)
{
return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0;
}

-static __always_inline bool folio_test_anon(struct folio *folio)
+static __always_inline bool folio_test_anon(const struct folio *folio)
{
return ((unsigned long)folio->mapping & PAGE_MAPPING_ANON) != 0;
}

-static __always_inline bool PageAnon(struct page *page)
+static __always_inline bool PageAnon(const struct page *page)
{
return folio_test_anon(page_folio(page));
}
@@ -669,7 +678,7 @@ static __always_inline bool __folio_test_movable(const struct folio *folio)
PAGE_MAPPING_MOVABLE;
}

-static __always_inline int __PageMovable(struct page *page)
+static __always_inline bool __PageMovable(const struct page *page)
{
return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
PAGE_MAPPING_MOVABLE;
@@ -682,13 +691,13 @@ static __always_inline int __PageMovable(struct page *page)
* is found in VM_MERGEABLE vmas. It's a PageAnon page, pointing not to any
* anon_vma, but to that page's node of the stable tree.
*/
-static __always_inline bool folio_test_ksm(struct folio *folio)
+static __always_inline bool folio_test_ksm(const struct folio *folio)
{
return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) ==
PAGE_MAPPING_KSM;
}

-static __always_inline bool PageKsm(struct page *page)
+static __always_inline bool PageKsm(const struct page *page)
{
return folio_test_ksm(page_folio(page));
}
@@ -708,9 +717,9 @@ u64 stable_page_flags(struct page *page);
* some of the bytes in it may be; see the is_partially_uptodate()
* address_space operation.
*/
-static inline bool folio_test_uptodate(struct folio *folio)
+static inline bool folio_test_uptodate(const struct folio *folio)
{
- bool ret = test_bit(PG_uptodate, folio_flags(folio, 0));
+ bool ret = test_bit(PG_uptodate, const_folio_flags(folio, 0));
/*
* Must ensure that the data we read out of the folio is loaded
* _after_ we've loaded folio->flags to check the uptodate bit.
@@ -725,7 +734,7 @@ static inline bool folio_test_uptodate(struct folio *folio)
return ret;
}

-static inline int PageUptodate(struct page *page)
+static inline bool PageUptodate(const struct page *page)
{
return folio_test_uptodate(page_folio(page));
}
@@ -777,12 +786,12 @@ static inline bool test_set_page_writeback(struct page *page)
return set_page_writeback(page);
}

-static __always_inline bool folio_test_head(struct folio *folio)
+static __always_inline bool folio_test_head(const struct folio *folio)
{
- return test_bit(PG_head, folio_flags(folio, FOLIO_PF_ANY));
+ return test_bit(PG_head, const_folio_flags(folio, FOLIO_PF_ANY));
}

-static __always_inline int PageHead(struct page *page)
+static __always_inline bool PageHead(const struct page *page)
{
PF_POISONED_CHECK(page);
return test_bit(PG_head, &page->flags) && !page_is_fake_head(page);
@@ -798,7 +807,7 @@ CLEARPAGEFLAG(Head, head, PF_ANY)
*
* Return: True if the folio is larger than one page.
*/
-static inline bool folio_test_large(struct folio *folio)
+static inline bool folio_test_large(const struct folio *folio)
{
return folio_test_head(folio);
}
@@ -824,9 +833,9 @@ static inline void ClearPageCompound(struct page *page)
#define PG_head_mask ((1UL << PG_head))

#ifdef CONFIG_HUGETLB_PAGE
-int PageHuge(struct page *page);
-int PageHeadHuge(struct page *page);
-static inline bool folio_test_hugetlb(struct folio *folio)
+bool PageHuge(const struct page *page);
+bool PageHeadHuge(const struct page *page);
+static inline bool folio_test_hugetlb(const struct folio *folio)
{
return PageHeadHuge(&folio->page);
}
@@ -844,13 +853,13 @@ TESTPAGEFLAG_FALSE(HeadHuge, headhuge)
* hugetlbfs pages, but not normal pages. PageTransHuge() can only be
* called only in the core VM paths where hugetlbfs pages can't exist.
*/
-static inline int PageTransHuge(struct page *page)
+static inline bool PageTransHuge(const struct page *page)
{
VM_BUG_ON_PAGE(PageTail(page), page);
return PageHead(page);
}

-static inline bool folio_test_transhuge(struct folio *folio)
+static inline bool folio_test_transhuge(const struct folio *folio)
{
return folio_test_head(folio);
}
@@ -860,7 +869,7 @@ static inline bool folio_test_transhuge(struct folio *folio)
* and hugetlbfs pages, so it should only be called when it's known
* that hugetlbfs pages aren't involved.
*/
-static inline int PageTransCompound(struct page *page)
+static inline bool PageTransCompound(const struct page *page)
{
return PageCompound(page);
}
@@ -870,7 +879,7 @@ static inline int PageTransCompound(struct page *page)
* and hugetlbfs pages, so it should only be called when it's known
* that hugetlbfs pages aren't involved.
*/
-static inline int PageTransTail(struct page *page)
+static inline bool PageTransTail(const struct page *page)
{
return PageTail(page);
}
@@ -918,7 +927,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
* best effort only and inherently racy: there is no way to synchronize with
* failing hardware.
*/
-static inline bool is_page_hwpoison(struct page *page)
+static inline bool is_page_hwpoison(const struct page *page)
{
if (PageHWPoison(page))
return true;
@@ -945,13 +954,13 @@ static inline bool is_page_hwpoison(struct page *page)
#define PageType(page, flag) \
((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)

-static inline int page_has_type(struct page *page)
+static inline bool page_has_type(const struct page *page)
{
return (int)page->page_type < PAGE_MAPCOUNT_RESERVE;
}

#define PAGE_TYPE_OPS(uname, lname) \
-static __always_inline int Page##uname(struct page *page) \
+static __always_inline bool Page##uname(const struct page *page) \
{ \
return PageType(page, PG_##lname); \
} \
@@ -1011,11 +1020,11 @@ PAGE_TYPE_OPS(Table, table)
*/
PAGE_TYPE_OPS(Guard, guard)

-extern bool is_free_buddy_page(struct page *page);
+extern bool is_free_buddy_page(const struct page *page);

PAGEFLAG(Isolated, isolated, PF_ANY);

-static __always_inline int PageAnonExclusive(struct page *page)
+static __always_inline bool PageAnonExclusive(const struct page *page)
{
VM_BUG_ON_PGFLAGS(!PageAnon(page), page);
VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
@@ -1080,12 +1089,12 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
* Determine if a page has private stuff, indicating that release routines
* should be invoked upon it.
*/
-static inline int page_has_private(struct page *page)
+static inline bool page_has_private(const struct page *page)
{
return !!(page->flags & PAGE_FLAGS_PRIVATE);
}

-static inline bool folio_has_private(struct folio *folio)
+static inline bool folio_has_private(const struct folio *folio)
{
return page_has_private(&folio->page);
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 546df97c31e4..ac8bed42f276 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1886,10 +1886,10 @@ static bool prep_compound_gigantic_page_for_demote(struct page *page,
* transparent huge pages. See the PageTransHuge() documentation for more
* details.
*/
-int PageHuge(struct page *page)
+bool PageHuge(const struct page *page)
{
if (!PageCompound(page))
- return 0;
+ return false;

page = compound_head(page);
return page[1].compound_dtor == HUGETLB_PAGE_DTOR;
@@ -1900,10 +1900,10 @@ EXPORT_SYMBOL_GPL(PageHuge);
* PageHeadHuge() only returns true for hugetlbfs head page, but not for
* normal or transparent huge pages.
*/
-int PageHeadHuge(struct page *page_head)
+bool PageHeadHuge(const struct page *page_head)
{
if (!PageHead(page_head))
- return 0;
+ return false;

return page_head[1].compound_dtor == HUGETLB_PAGE_DTOR;
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 218b28ee49ed..81ccca8364bb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9586,13 +9586,13 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
/*
* This function returns a stable result only if called under zone lock.
*/
-bool is_free_buddy_page(struct page *page)
+bool is_free_buddy_page(const struct page *page)
{
unsigned long pfn = page_to_pfn(page);
unsigned int order;

for (order = 0; order < MAX_ORDER; order++) {
- struct page *page_head = page - (pfn & ((1 << order) - 1));
+ const struct page *page_head = page - (pfn & ((1 << order) - 1));

if (PageBuddy(page_head) &&
buddy_order_unsafe(page_head) >= order)