+ mm-allow-for-detecting-underflows-with-page_mapcount-again-fix.patch added to mm-unstable branch

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

The patch titled
     Subject: mm-allow-for-detecting-underflows-with-page_mapcount-again-fix
has been added to the -mm mm-unstable branch.  Its filename is
     mm-allow-for-detecting-underflows-with-page_mapcount-again-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-allow-for-detecting-underflows-with-page_mapcount-again-fix.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: David Hildenbrand <david@redhat.com>
Subject: mm-allow-for-detecting-underflows-with-page_mapcount-again-fix
Date: Wed, 24 Apr 2024 10:50:09 +0200

Let's make page_mapcount() slighly more efficient by inlining the
page_type_has_type() check.

Link: https://lkml.kernel.org/r/1af4fd61-7926-47c8-be45-833c0dbec08b@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Richard Chang <richardycc@google.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/include/linux/mm.h~mm-allow-for-detecting-underflows-with-page_mapcount-again-fix
+++ a/include/linux/mm.h
@@ -1229,10 +1229,11 @@ static inline void page_mapcount_reset(s
  */
 static inline int page_mapcount(struct page *page)
 {
-	int mapcount = atomic_read(&page->_mapcount);
+	int mapcount = atomic_read(&page->_mapcount) + 1;
 
 	/* Handle page_has_type() pages */
-	mapcount = page_type_has_type(mapcount) ? 0 : mapcount + 1;
+	if (mapcount < PAGE_MAPCOUNT_RESERVE + 1)
+		mapcount = 0;
 	if (unlikely(PageCompound(page)))
 		mapcount += folio_entire_mapcount(page_folio(page));
 
_

Patches currently in -mm which might be from david@redhat.com are

mm-madvise-dont-perform-madvise-vma-walk-for-madv_populate_readwrite.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared-fix.patch
selftests-memfd_secret-add-vmsplice-test.patch
mm-merge-folio_is_secretmem-and-folio_fast_pin_allowed-into-gup_fast_folio_allowed.patch
mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch
mm-remove-prot-parameter-from-move_pte.patch
mm-gup-consistently-name-gup-fast-functions.patch
mm-treewide-rename-config_have_fast_gup-to-config_have_gup_fast.patch
mm-use-gup-fast-instead-fast-gup-in-remaining-comments.patch
drivers-virt-acrn-fix-pfnmap-pte-checks-in-acrn_vm_ram_map.patch
mm-pass-vma-instead-of-mm-to-follow_pte.patch
mm-follow_pte-improvements.patch
mm-allow-for-detecting-underflows-with-page_mapcount-again.patch
mm-allow-for-detecting-underflows-with-page_mapcount-again-fix.patch
mm-rmap-always-inline-anon-file-rmap-duplication-of-a-single-pte.patch
mm-rmap-add-fast-path-for-small-folios-when-adding-removing-duplicating.patch
mm-track-mapcount-of-large-folios-in-single-value.patch
mm-improve-folio_likely_mapped_shared-using-the-mapcount-of-large-folios.patch
mm-make-folio_mapcount-return-0-for-small-typed-folios.patch
mm-make-folio_mapcount-return-0-for-small-typed-folios-fix.patch
mm-memory-use-folio_mapcount-in-zap_present_folio_ptes.patch
mm-huge_memory-use-folio_mapcount-in-zap_huge_pmd-sanity-check.patch
mm-memory-failure-use-folio_mapcount-in-hwpoison_user_mappings.patch
mm-page_alloc-use-folio_mapped-in-__alloc_contig_migrate_range.patch
mm-migrate-use-folio_likely_mapped_shared-in-add_page_for_migration.patch
sh-mm-cache-use-folio_mapped-in-copy_from_user_page.patch
mm-filemap-use-folio_mapcount-in-filemap_unaccount_folio.patch
mm-migrate_device-use-folio_mapcount-in-migrate_vma_check_page.patch
trace-events-page_ref-trace-the-raw-page-mapcount-value.patch
xtensa-mm-convert-check_tlb_entry-to-sanity-check-folios.patch
mm-debug-print-only-page-mapcount-excluding-folio-entire-mapcount-in-__dump_folio.patch
documentation-admin-guide-cgroup-v1-memoryrst-dont-reference-page_mapcount.patch
mm-ksm-rename-get_ksm_page_flags-to-ksm_get_folio_flags.patch
mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.patch
fs-proc-task_mmu-convert-pagemap_hugetlb_range-to-work-on-folios.patch
fs-proc-task_mmu-convert-smaps_hugetlb_range-to-work-on-folios.patch
mm-huge_memory-improve-split_huge_page_to_list_to_order-return-value-documentation.patch
mm-huge_memory-improve-split_huge_page_to_list_to_order-return-value-documentation-v2.patch
mm-khugepaged-replace-page_mapcount-check-by-folio_likely_mapped_shared.patch
loongarch-tlb-fix-error-parameter-ptep-set-but-not-used-due-to-__tlb_remove_tlb_entry.patch