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From fd1a745ce03e37945674c14833870a9af0882e2d Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Thu, 21 Mar 2024 14:24:42 +0000
Subject: mm: support page_mapcount() on page_has_type() pages
From: Matthew Wilcox (Oracle) <willy@infradead.org>
commit fd1a745ce03e37945674c14833870a9af0882e2d upstream.
Return 0 for pages which can't be mapped. This matches how page_mapped()
works. It is more convenient for users to not have to filter out these
pages.
Link: https://lkml.kernel.org/r/20240321142448.1645400-5-willy@infradead.org
Fixes: 9c5ccf2db04b ("mm: remove HUGETLB_PAGE_DTOR")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/proc/page.c | 7 ++-----
include/linux/mm.h | 8 +++++---
include/linux/page-flags.h | 4 ++--
3 files changed, 9 insertions(+), 10 deletions(-)
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -67,7 +67,7 @@ static ssize_t kpagecount_read(struct fi
*/
ppage = pfn_to_online_page(pfn);
- if (!ppage || PageSlab(ppage) || page_has_type(ppage))
+ if (!ppage)
pcount = 0;
else
pcount = page_mapcount(ppage);
@@ -124,11 +124,8 @@ u64 stable_page_flags(struct page *page)
/*
* pseudo flags for the well known (anonymous) memory mapped pages
- *
- * Note that page->_mapcount is overloaded in SLAB, so the
- * simple test in page_mapped() is not enough.
*/
- if (!PageSlab(page) && page_mapped(page))
+ if (page_mapped(page))
u |= 1 << KPF_MMAP;
if (PageAnon(page))
u |= 1 << KPF_ANON;
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1204,14 +1204,16 @@ static inline void page_mapcount_reset(s
* a large folio, it includes the number of times this page is mapped
* as part of that folio.
*
- * The result is undefined for pages which cannot be mapped into userspace.
- * For example SLAB or special types of pages. See function page_has_type().
- * They use this field in struct page differently.
+ * Will report 0 for pages which cannot be mapped into userspace, eg
+ * slab, page tables and similar.
*/
static inline int page_mapcount(struct page *page)
{
int mapcount = atomic_read(&page->_mapcount) + 1;
+ /* Handle page_has_type() pages */
+ if (mapcount < 0)
+ mapcount = 0;
if (unlikely(PageCompound(page)))
mapcount += folio_entire_mapcount(page_folio(page));
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -945,12 +945,12 @@ static inline bool is_page_hwpoison(stru
* page_type may be used. Because it is initialised to -1, we invert the
* sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and
* __ClearPageFoo *sets* the bit used for PageFoo. We reserve a few high and
- * low bits so that an underflow or overflow of page_mapcount() won't be
+ * low bits so that an underflow or overflow of _mapcount won't be
* mistaken for a page type value.
*/
#define PAGE_TYPE_BASE 0xf0000000
-/* Reserve 0x0000007f to catch underflows of page_mapcount */
+/* Reserve 0x0000007f to catch underflows of _mapcount */
#define PAGE_MAPCOUNT_RESERVE -128
#define PG_buddy 0x00000080
#define PG_offline 0x00000100
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