On 2024/8/6 17:29, David Hildenbrand wrote:
> On 02.08.24 09:50, Kefeng Wang wrote:
>>
>>
>> On 2024/8/2 4:10, David Hildenbrand wrote:
>>>
>>>>>
>>>>> We're not checking the head page here, will this work reliably for
>>>>> hugetlb? (I recall some difference in per-page hwpoison handling between
>>>>> hugetlb and THP due to the vmemmap optimization)
>>>>
>>>> Before this changes, the hwposioned hugetlb page won't try to unmap in
>>>> do_migrate_range(), we hope it already unmapped in memory_failure(), as
>>>> mentioned from comments, there maybe fail to unmap, so a new safeguard
>>>> to try to unmap it again here, but we don't need to guarantee it.
>>>
>>> Thanks for clarifying!
>>>
>>> But I do wonder if the PageHWPoison() is the right thing to do for hugetlb.
>>>
>>> IIUC, hugetlb requires folio_test_hwpoison() -- testing the head page
>>> not the subpage. Reason is that due to the vmemmap optimization we might
>>> not be able to modify subpages to set hwpoison.
>>
>> Yes, HVO is special(only head page with hwpoison), since we always want
>> to check head page here (next pfn = head_pfn + nr), so it might be
>> enough to only use PageHWpoison, but just in case, adding hwpoison check
>> for the head page,
>>
>> if (unlikely(PageHWPoison(page) || folio_test_hwpoison(folio)))
>
> I also do wonder if we have to check for large folios folio_test_has_hwpoison():
> if any subpage is poisoned, not just the current page.
>
IMHO, below if condition [1] should be fine to check for any hwpoisoned folio:
if (folio_test_hwpoison(folio) ||
(folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
1. For raw pages, folio_test_hwpoison(folio) works fine.
2. For thp (memory_failure fails to split it in first place), folio_test_has_hwpoisoned(folio) works fine.
3. For hugetlb, we always have hwpoison flag set for folio. So folio_test_hwpoison(folio) works fine.
But folio might not be the right hwpoisoned page, i.e. subpages might be hwpoisoned instead.
Or am I miss something?
[1] https://lore.kernel.org/linux-mm/234b0b85-cbf1-4af4-85c9-ac0d00ceeed2@xxxxxxx/T/#m799ab8095c72018651923921339c3519078c64af
Thanks.
.
