linux-kernel - [PATCH v3] mm: convert page type macros to enum

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Date: Thu,  6 Jun 2024 17:11:15 -0700
From: Stephen Brennan <stephen.s.brennan@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Vishal Moola (Oracle)" <vishal.moola@...il.com>, linux-mm@...ck.org,
        Omar Sandoval <osandov@...ndov.com>, linux-debuggers@...r.kernel.org,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Stephen Brennan <stephen.s.brennan@...cle.com>,
        David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        Hao Ge <gehao@...inos.cn>, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v3] mm: convert page type macros to enum

Changing PG_slab from a page flag to a page type in commit 46df8e73a4a3
("mm: free up PG_slab") in has the unintended consequence of removing
the PG_slab constant from kernel debuginfo. The commit does add the
value to the vmcoreinfo note, which allows debuggers to find the value
without hardcoding it. However it's most flexible to continue
representing the constant with an enum. To that end, convert the page
type fields into an enum. Debuggers will now be able to detect that
PG_slab's type has changed from enum pageflags to enum page_type.

Fixes: 46df8e73a4a3 ("mm: free up PG_slab")

Signed-off-by: Stephen Brennan <stephen.s.brennan@...cle.com>
---
v2 -> v3: rebase on mm-unstable
v1 -> v2: include PAGE_TYPE_BASE and PAGE_MAPCOUNT_RESERVE

 include/linux/page-flags.h | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index f04fea86324d9..7c0a8fd2c8c17 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -945,20 +945,23 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
  * mistaken for a page type value.
  */
 
-#define PAGE_TYPE_BASE	0x80000000
-/*
- * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and
- * allow owners that set a type to reuse the lower 16 bit for their own
- * purposes.
- */
-#define PG_buddy	0x40000000
-#define PG_offline	0x20000000
-#define PG_table	0x10000000
-#define PG_guard	0x08000000
-#define PG_hugetlb	0x04000000
-#define PG_slab		0x02000000
-#define PG_zsmalloc	0x01000000
-#define PAGE_MAPCOUNT_RESERVE	(~0x0000ffff)
+enum page_type {
+	/*
+	 * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and
+	 * allow owners that set a type to reuse the lower 16 bit for their own
+	 * purposes.
+	 */
+	PG_buddy	= 0x40000000,
+	PG_offline	= 0x20000000,
+	PG_table	= 0x10000000,
+	PG_guard	= 0x08000000,
+	PG_hugetlb	= 0x04000000,
+	PG_slab		= 0x02000000,
+	PG_zsmalloc	= 0x01000000,
+
+	PAGE_TYPE_BASE	= 0x80000000,
+	PAGE_MAPCOUNT_RESERVE	= ~0x0000ffff,
+};
 
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
-- 
2.43.0