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authorMike Kravetz <mike.kravetz@oracle.com>2023-01-26 14:27:20 -0800
committerAndrew Morton <akpm@linux-foundation.org>2023-01-31 16:44:09 -0800
commit3489dbb696d25602aea8c3e669a6d43b76bd5358 (patch)
tree1839fd52a4146e534785c9f830278e6b1525768d /fs/proc
parentedb5d0cf5525357652aff6eacd9850b8ced07143 (diff)
mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps
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. [akpm@linux-foundation.org: simplification, per David] [akpm@linux-foundation.org: hugetlb.h: include page_ref.h for page_count()] 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> Acked-by: Peter Xu <peterx@redhat.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: 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>
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/task_mmu.c4
1 files changed, 1 insertions, 3 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e35a0398db63..af1c49ae11b1 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -745,9 +745,7 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
page = pfn_swap_entry_to_page(swpent);
}
if (page) {
- int mapcount = page_mapcount(page);
-
- if (mapcount >= 2)
+ if (page_mapcount(page) >= 2 || hugetlb_pmd_shared(pte))
mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
else
mss->private_hugetlb += huge_page_size(hstate_vma(vma));