From: Mike Kravetz mike.kravetz@oracle.com
commit 3489dbb696d25602aea8c3e669a6d43b76bd5358 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/proc/task_mmu.c | 4 +--- include/linux/hugetlb.h | 13 +++++++++++++ 2 files changed, 14 insertions(+), 3 deletions(-)
--- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -714,9 +714,7 @@ static int smaps_hugetlb_range(pte_t *pt page = device_private_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)); --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -7,6 +7,7 @@ #include <linux/fs.h> #include <linux/hugetlb_inline.h> #include <linux/cgroup.h> +#include <linux/page_ref.h> #include <linux/list.h> #include <linux/kref.h> #include <linux/pgtable.h> @@ -942,4 +943,16 @@ static inline __init void hugetlb_cma_ch } #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 + #endif /* _LINUX_HUGETLB_H */