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

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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no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT.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: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-03-03 17:30:11 +01:00 committed by Andrew Morton
parent eb16876971
commit 7a34ae1449
2 changed files with 11 additions and 1 deletions
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5
Documentation/filesystems/proc.rst
View File

@ -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
---------------

7
fs/proc/task_mmu.c
View File

@ -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))