Commit 7a34ae14 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

fs/proc/task_mmu: remove per-page mapcount dependency for "mapmax" (CONFIG_NO_PAGE_MAPCOUNT) 

Let's implement an alternative when per-page mapcounts in large folios are
no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT.

For calculating "mapmax", we now use the average per-page mapcount in a
large folio instead of the per-page mapcount.

For hugetlb folios and folios that are not partially mapped into MMs,
there is no change.

Likely, this change will not matter much in practice, and an alternative
might be to simple remove this stat with CONFIG_NO_PAGE_MAPCOUNT. 
However, there might be value to it, so let's keep it like that and
document the behavior.

Link: https://lkml.kernel.org/r/20250303163014.1128035-19-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Andy Lutomirks^H^Hski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michal Koutn <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: tejun heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent eb168769

Documentation/filesystems/proc.rst

+5 −0
Original line number Diff line number Diff line
@@ -686,6 +686,11 @@ Where: 
node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page

size, in KB, that is backing the mapping up.



Note that some kernel configurations do not track the precise number of times

a page part of a larger allocation (e.g., THP) is mapped. In these

configurations, "mapmax" might corresponds to the average number of mappings

per page in such a larger allocation instead.



1.2 Kernel data

---------------

fs/proc/task_mmu.c

+6 −1
Original line number Diff line number Diff line
@@ -2863,7 +2863,12 @@ static void gather_stats(struct page *page, struct numa_maps *md, int pte_dirty, 
			unsigned long nr_pages)

{

	struct folio *folio = page_folio(page);

	int count = folio_precise_page_mapcount(folio, page);

	int count;



	if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))

		count = folio_precise_page_mapcount(folio, page);

	else

		count = folio_average_page_mapcount(folio);



	md->pages += nr_pages;

	if (pte_dirty || folio_test_dirty(folio))