+ mm-introduce-page_mapcount_is_type.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: introduce page_mapcount_is_type()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-introduce-page_mapcount_is_type.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-introduce-page_mapcount_is_type.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm: introduce page_mapcount_is_type()
Date: Wed, 21 Aug 2024 18:39:10 +0100

Resolve the awkward "and add one to this opaque constant" test into a
self-documenting inline function.

Link: https://lkml.kernel.org/r/20240821173914.2270383-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/internal.h         |    3 +--
 include/linux/mm.h         |    3 +--
 include/linux/page-flags.h |   12 +++++++++---
 3 files changed, 11 insertions(+), 7 deletions(-)

--- a/fs/proc/internal.h~mm-introduce-page_mapcount_is_type
+++ a/fs/proc/internal.h
@@ -166,8 +166,7 @@ static inline int folio_precise_page_map
 {
 	int mapcount = atomic_read(&page->_mapcount) + 1;
 
-	/* Handle page_has_type() pages */
-	if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
+	if (page_mapcount_is_type(mapcount))
 		mapcount = 0;
 	if (folio_test_large(folio))
 		mapcount += folio_entire_mapcount(folio);
--- a/include/linux/mm.h~mm-introduce-page_mapcount_is_type
+++ a/include/linux/mm.h
@@ -1228,8 +1228,7 @@ static inline int folio_mapcount(const s
 
 	if (likely(!folio_test_large(folio))) {
 		mapcount = atomic_read(&folio->_mapcount) + 1;
-		/* Handle page_has_type() pages */
-		if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
+		if (page_mapcount_is_type(mapcount))
 			mapcount = 0;
 		return mapcount;
 	}
--- a/include/linux/page-flags.h~mm-introduce-page_mapcount_is_type
+++ a/include/linux/page-flags.h
@@ -956,12 +956,18 @@ enum pagetype {
 #define folio_test_type(folio, flag)					\
 	((READ_ONCE(folio->page.page_type) & (PAGE_TYPE_BASE | flag))  == PAGE_TYPE_BASE)
 
-static inline int page_type_has_type(unsigned int page_type)
+static inline bool page_type_has_type(int page_type)
 {
-	return (int)page_type < PAGE_MAPCOUNT_RESERVE;
+	return page_type < PAGE_MAPCOUNT_RESERVE;
 }
 
-static inline int page_has_type(const struct page *page)
+/* This takes a mapcount which is one more than page->_mapcount */
+static inline bool page_mapcount_is_type(unsigned int mapcount)
+{
+	return page_type_has_type(mapcount - 1);
+}
+
+static inline bool page_has_type(const struct page *page)
 {
 	return page_type_has_type(READ_ONCE(page->page_type));
 }
_

Patches currently in -mm which might be from willy@infradead.org are

fs-remove-calls-to-set-and-clear-the-folio-error-flag.patch
mm-remove-pg_error.patch
mm-return-the-folio-from-swapin_readahead.patch
printf-remove-%pgt-support.patch
mm-introduce-page_mapcount_is_type.patch
mm-support-only-one-page_type-per-page.patch
zsmalloc-use-all-available-24-bits-of-page_type.patch