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>

Author: Matthew Wilcox (Oracle)

arch/arc/mm/cache.c

@@ -704,7 +704,7 @@ static inline void arc_slc_enable(void)
 
 void flush_dcache_folio(struct folio *folio)
 {
-	clear_bit(PG_dc_clean, &folio->flags);
+	clear_bit(PG_dc_clean, &folio->flags.f);
 	return;
 }
 EXPORT_SYMBOL(flush_dcache_folio);
@@ -889,8 +889,8 @@ void copy_user_highpage(struct page *to, struct page *from,
 
 	copy_page(kto, kfrom);
 
-	clear_bit(PG_dc_clean, &dst->flags);
-	clear_bit(PG_dc_clean, &src->flags);
+	clear_bit(PG_dc_clean, &dst->flags.f);
+	clear_bit(PG_dc_clean, &src->flags.f);
 
 	kunmap_atomic(kto);
 	kunmap_atomic(kfrom);
@@ -900,7 +900,7 @@ void clear_user_page(void *to, unsigned long u_vaddr, struct page *page)
 {
 	struct folio *folio = page_folio(page);
 	clear_page(to);
-	clear_bit(PG_dc_clean, &folio->flags);
+	clear_bit(PG_dc_clean, &folio->flags.f);
 }
 EXPORT_SYMBOL(clear_user_page);
 

arch/arc/mm/tlb.c

@@ -488,7 +488,7 @@ void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma,
 	 */
 	if (vma->vm_flags & VM_EXEC) {
 		struct folio *folio = page_folio(page);
-		int dirty = !test_and_set_bit(PG_dc_clean, &folio->flags);
+		int dirty = !test_and_set_bit(PG_dc_clean, &folio->flags.f);
 		if (dirty) {
 			unsigned long offset = offset_in_folio(folio, paddr);
 			nr = folio_nr_pages(folio);

arch/arm/include/asm/hugetlb.h

@@ -17,7 +17,7 @@
 
 static inline void arch_clear_hugetlb_flags(struct folio *folio)
 {
-	clear_bit(PG_dcache_clean, &folio->flags);
+	clear_bit(PG_dcache_clean, &folio->flags.f);
 }
 #define arch_clear_hugetlb_flags arch_clear_hugetlb_flags
 

arch/arm/mm/copypage-v4mc.c

@@ -67,7 +67,7 @@ void v4_mc_copy_user_highpage(struct page *to, struct page *from,
 	struct folio *src = page_folio(from);
 	void *kto = kmap_atomic(to);
 
-	if (!test_and_set_bit(PG_dcache_clean, &src->flags))
+	if (!test_and_set_bit(PG_dcache_clean, &src->flags.f))
 		__flush_dcache_folio(folio_flush_mapping(src), src);
 
 	raw_spin_lock(&minicache_lock);

arch/arm/mm/copypage-v6.c

@@ -73,7 +73,7 @@ static void v6_copy_user_highpage_aliasing(struct page *to,
 	unsigned int offset = CACHE_COLOUR(vaddr);
 	unsigned long kfrom, kto;
 
-	if (!test_and_set_bit(PG_dcache_clean, &src->flags))
+	if (!test_and_set_bit(PG_dcache_clean, &src->flags.f))
 		__flush_dcache_folio(folio_flush_mapping(src), src);
 
 	/* FIXME: not highmem safe */

arch/arm/mm/copypage-xscale.c

@@ -87,7 +87,7 @@ void xscale_mc_copy_user_highpage(struct page *to, struct page *from,
 	struct folio *src = page_folio(from);
 	void *kto = kmap_atomic(to);
 
-	if (!test_and_set_bit(PG_dcache_clean, &src->flags))
+	if (!test_and_set_bit(PG_dcache_clean, &src->flags.f))
 		__flush_dcache_folio(folio_flush_mapping(src), src);
 
 	raw_spin_lock(&minicache_lock);

arch/arm/mm/dma-mapping.c

@@ -718,7 +718,7 @@ static void __dma_page_dev_to_cpu(struct page *page, unsigned long off,
 			if (size < sz)
 				break;
 			if (!offset)
-				set_bit(PG_dcache_clean, &folio->flags);
+				set_bit(PG_dcache_clean, &folio->flags.f);
 			offset = 0;
 			size -= sz;
 			if (!size)

arch/arm/mm/fault-armv.c

@@ -203,7 +203,7 @@ void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma,
 
 	folio = page_folio(pfn_to_page(pfn));
 	mapping = folio_flush_mapping(folio);
-	if (!test_and_set_bit(PG_dcache_clean, &folio->flags))
+	if (!test_and_set_bit(PG_dcache_clean, &folio->flags.f))
 		__flush_dcache_folio(mapping, folio);
 	if (mapping) {
 		if (cache_is_vivt())

arch/arm/mm/flush.c

@@ -304,7 +304,7 @@ void __sync_icache_dcache(pte_t pteval)
 	else
 		mapping = NULL;
 
-	if (!test_and_set_bit(PG_dcache_clean, &folio->flags))
+	if (!test_and_set_bit(PG_dcache_clean, &folio->flags.f))
 		__flush_dcache_folio(mapping, folio);
 
 	if (pte_exec(pteval))
@@ -343,23 +343,23 @@ void flush_dcache_folio(struct folio *folio)
 		return;
 
 	if (!cache_ops_need_broadcast() && cache_is_vipt_nonaliasing()) {
-		if (test_bit(PG_dcache_clean, &folio->flags))
-			clear_bit(PG_dcache_clean, &folio->flags);
+		if (test_bit(PG_dcache_clean, &folio->flags.f))
+			clear_bit(PG_dcache_clean, &folio->flags.f);
 		return;
 	}
 
 	mapping = folio_flush_mapping(folio);
 
 	if (!cache_ops_need_broadcast() &&
 	    mapping && !folio_mapped(folio))
-		clear_bit(PG_dcache_clean, &folio->flags);
+		clear_bit(PG_dcache_clean, &folio->flags.f);
 	else {
 		__flush_dcache_folio(mapping, folio);
 		if (mapping && cache_is_vivt())
 			__flush_dcache_aliases(mapping, folio);
 		else if (mapping)
 			__flush_icache_all();
-		set_bit(PG_dcache_clean, &folio->flags);
+		set_bit(PG_dcache_clean, &folio->flags.f);
 	}
 }
 EXPORT_SYMBOL(flush_dcache_folio);

arch/arm64/include/asm/hugetlb.h

@@ -21,12 +21,12 @@ extern bool arch_hugetlb_migration_supported(struct hstate *h);
 
 static inline void arch_clear_hugetlb_flags(struct folio *folio)
 {
-	clear_bit(PG_dcache_clean, &folio->flags);
+	clear_bit(PG_dcache_clean, &folio->flags.f);
 
 #ifdef CONFIG_ARM64_MTE
 	if (system_supports_mte()) {
-		clear_bit(PG_mte_tagged, &folio->flags);
-		clear_bit(PG_mte_lock, &folio->flags);
+		clear_bit(PG_mte_tagged, &folio->flags.f);
+		clear_bit(PG_mte_lock, &folio->flags.f);
 	}
 #endif
 }