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, 6 insertions, 6 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2ee21e46f0fb..ca9e6b9633f7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -950,7 +950,7 @@ static inline void __free_one_page(struct page *page,
 	bool to_tail;
 
 	VM_BUG_ON(!zone_is_initialized(zone));
-	VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
+	VM_BUG_ON_PAGE(page->flags.f & PAGE_FLAGS_CHECK_AT_PREP, page);
 
 	VM_BUG_ON(migratetype == -1);
 	VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
@@ -1043,7 +1043,7 @@ static inline bool page_expected_state(struct page *page,
 			page->memcg_data |
 #endif
 			page_pool_page_is_pp(page) |
-			(page->flags & check_flags)))
+			(page->flags.f & check_flags)))
 		return false;
 
 	return true;
@@ -1059,7 +1059,7 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
 		bad_reason = "non-NULL mapping";
 	if (unlikely(page_ref_count(page) != 0))
 		bad_reason = "nonzero _refcount";
-	if (unlikely(page->flags & flags)) {
+	if (unlikely(page->flags.f & flags)) {
 		if (flags == PAGE_FLAGS_CHECK_AT_PREP)
 			bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag(s) set";
 		else
@@ -1358,7 +1358,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 		int i;
 
 		if (compound) {
-			page[1].flags &= ~PAGE_FLAGS_SECOND;
+			page[1].flags.f &= ~PAGE_FLAGS_SECOND;
 #ifdef NR_PAGES_IN_LARGE_FOLIO
 			folio->_nr_pages = 0;
 #endif
@@ -1372,7 +1372,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 					continue;
 				}
 			}
-			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+			(page + i)->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
 	if (folio_test_anon(folio)) {
@@ -1391,7 +1391,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 	}
 
 	page_cpupid_reset_last(page);
-	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+	page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
 	reset_page_owner(page, order);
 	page_table_check_free(page, order);
 	pgalloc_tag_sub(page, 1 << order);