Commit fd1a745c authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: support page_mapcount() on page_has_type() pages 

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: 9c5ccf2d ("mm: remove HUGETLB_PAGE_DTOR")
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarVlastimil 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 12bbaae7

fs/proc/page.c

+2 −5
Original line number Diff line number Diff line
@@ -67,7 +67,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, 
		 */

		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;

include/linux/mm.h

+5 −3
Original line number Diff line number Diff line
@@ -1223,14 +1223,16 @@ static inline void page_mapcount_reset(struct page *page) 
 * 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));

include/linux/page-flags.h

+2 −2
Original line number Diff line number Diff line
@@ -971,12 +971,12 @@ static inline bool is_page_hwpoison(struct page *page) 
 * 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