The patch titled Subject: mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Mike Kravetz mike.kravetz@oracle.com Subject: mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps Date: Thu, 26 Jan 2023 14:27:20 -0800

Patch series "Fixes for hugetlb mapcount at most 1 for shared PMDs".

This issue of mapcount in hugetlb pages referenced by shared PMDs was discussed in [1]. The following two patches address user visible behavior caused by this issue.

[1] https://lore.kernel.org/linux-mm/Y9BF+OCdWnCSilEu@monkey/

This patch (of 2):

A hugetlb page will have a mapcount of 1 if mapped by multiple processes via a shared PMD. This is because only the first process increases the map count, and subsequent processes just add the shared PMD page to their page table.

page_mapcount is being used to decide if a hugetlb page is shared or private in /proc/PID/smaps. Pages referenced via a shared PMD were incorrectly being counted as private.

To fix, check for a shared PMD if mapcount is 1. If a shared PMD is found count the hugetlb page as shared. A new helper to check for a shared PMD is added.

Link: https://lkml.kernel.org/r/20230126222721.222195-2-mike.kravetz@oracle.com Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Cc: David Hildenbrand david@redhat.com Cc: James Houghton jthoughton@google.com Cc: Matthew Wilcox willy@infradead.org Cc: Michal Hocko mhocko@suse.com Cc: Muchun Song songmuchun@bytedance.com Cc: Naoya Horiguchi naoya.horiguchi@linux.dev Cc: Peter Xu peterx@redhat.com Cc: Vishal Moola (Oracle) vishal.moola@gmail.com Cc: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/proc/task_mmu.c | 10 ++++++++-- include/linux/hugetlb.h | 12 ++++++++++++ 2 files changed, 20 insertions(+), 2 deletions(-)

--- a/fs/proc/task_mmu.c~mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps +++ a/fs/proc/task_mmu.c @@ -749,8 +749,14 @@ static int smaps_hugetlb_range(pte_t *pt

if (mapcount >= 2) mss->shared_hugetlb += huge_page_size(hstate_vma(vma)); - else - mss->private_hugetlb += huge_page_size(hstate_vma(vma)); + else { + if (hugetlb_pmd_shared(pte)) + mss->shared_hugetlb += + huge_page_size(hstate_vma(vma)); + else + mss->private_hugetlb += + huge_page_size(hstate_vma(vma)); + } } return 0; } --- a/include/linux/hugetlb.h~mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps +++ a/include/linux/hugetlb.h @@ -1187,6 +1187,18 @@ static inline __init void hugetlb_cma_re } #endif

+#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE +static inline bool hugetlb_pmd_shared(pte_t *pte) +{ + return page_count(virt_to_page(pte)) > 1; +} +#else +static inline bool hugetlb_pmd_shared(pte_t *pte) +{ + return false; +} +#endif + bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr);

#ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE _

Patches currently in -mm which might be from mike.kravetz@oracle.com are

mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps.patch migrate-hugetlb-check-for-hugetlb-shared-pmd-in-node-migration.patch