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SubjectRe: [PATCH v1] mm, pagemap: expose hwpoison entry
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On 04.10.21 13:50, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
>
> A hwpoison entry is a non-present page table entry to report
> memory error events to userspace. If we have an easy way to know
> which processes have hwpoison entries, that might be useful for
> user processes to take proper actions. But we don't have it now.
> So make pagemap interface expose hwpoison entries to userspace.

Noting that this is only a way to inspect hwpoison set for private
anonymous memory. You cannot really identify anything related to shared
memory.

Do you also handle private hugetlb pages?

>
> Hwpoison entry for hugepage is also exposed by this patch. The below
> example shows how pagemap is visible in the case where a memory error
> hit a hugepage mapped to a process.
>
> $ ./page-types --no-summary --pid $PID --raw --list --addr 0x700000000+0x400
> voffset offset len flags
> 700000000 12fa00 1 ___U_______Ma__H_G_________________f_______1
> 700000001 12fa01 1ff ___________Ma___TG_________________f_______1
> 700000200 12f800 1 __________B________X_______________f______w_
> 700000201 12f801 1 ___________________X_______________f______w_ // memory failure hit this page
> 700000202 12f802 1fe __________B________X_______________f______w_
>
> The entries with both of "X" flag (hwpoison flag) and "w" flag (swap
> flag) are considered as hwpoison entries. So all pages in 2MB range
> are inaccessible from the process. We can get actual error location
> by page-types in physical address mode.
>
> $ ./page-types --no-summary --addr 0x12f800+0x200 --raw --list
> offset len flags
> 12f800 1 __________B_________________________________
> 12f801 1 ___________________X________________________
> 12f802 1fe __________B_________________________________
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> ---
> fs/proc/task_mmu.c | 41 ++++++++++++++++++++++++++++++++---------
> include/linux/swapops.h | 13 +++++++++++++
> tools/vm/page-types.c | 7 ++++++-
> 3 files changed, 51 insertions(+), 10 deletions(-)


Please also update the documentation located at

Documentation/admin-guide/mm/pagemap.rst


--
Thanks,

David / dhildenb

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