Re: [PATCH v2 3/5] mm: memory_hotplug: check hwpoisoned page firstly in do_migrate_range()

[David Hildenbrand <david@redhat.com>]

On 27.08.24 04:12, Miaohe Lin wrote:
> On 2024/8/27 9:13, Kefeng Wang wrote:
>>
>>
>> On 2024/8/26 22:46, David Hildenbrand wrote:
>>> On 17.08.24 10:49, Kefeng Wang wrote:
>>>> The commit b15c87263a69 ("hwpoison, memory_hotplug: allow hwpoisoned
>>>> pages to be offlined") don't handle the hugetlb pages, the endless
>>>> loop still occur if offline a hwpoison hugetlb, luckly, with the
>>>> commit e591ef7d96d6 ("mm,hwpoison,hugetlb,memory_hotplug: hotremove
>>>> memory section with hwpoisoned hugepage") section with hwpoisoned
>>>> hugepage"), the HPageMigratable of hugetlb page will be clear, and
>>>> the hwpoison hugetlb page will be skipped in scan_movable_pages(),
>>>> so the endless loop issue is fixed.
>>>>
>>>> However if the HPageMigratable() check passed(without reference and
>>>> lock), the hugetlb page may be hwpoisoned, it won't cause issue since
>>>> the hwpoisoned page will be handled correctly in the next movable
>>>> pages scan loop, and it will be isolated in do_migrate_range() but
>>>> fails to migrate. In order to avoid the unnecessary isolation and
>>>> unify all hwpoisoned page handling, let's unconditionally check hwpoison
>>>> firstly, and if it is a hwpoisoned hugetlb page, try to unmap it as
>>>> the catch all safety net like normal page does.
>>>>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>> ---
>>>>    mm/memory_hotplug.c | 17 +++++++++--------
>>>>    1 file changed, 9 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>> index dc19b0e28fbc..02a0d4fbc3fe 100644
>>>> --- a/mm/memory_hotplug.c
>>>> +++ b/mm/memory_hotplug.c
>>>> @@ -1793,13 +1793,8 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>>>>             * but out loop could handle that as it revisits the split
>>>>             * folio later.
>>>>             */
>>>> -        if (folio_test_large(folio)) {
>>>> +        if (folio_test_large(folio))
>>>>                pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
>>>> -            if (folio_test_hugetlb(folio)) {
>>>> -                isolate_hugetlb(folio, &source);
>>>> -                continue;
>>>> -            }
>>>> -        }
>>>>            /*
>>>>             * HWPoison pages have elevated reference counts so the migration would
>>>> @@ -1808,11 +1803,17 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>>>>             * (e.g. current hwpoison implementation doesn't unmap KSM pages but keep
>>>>             * the unmap as the catch all safety net).
>>>>             */
>>>> -        if (PageHWPoison(page)) {
>>>> +        if (folio_test_hwpoison(folio) ||
>>>> +            (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
>>>
>>> We have the exact same check already in mm/shmem.c now.
>>>
>>> Likely this should be factored out ... but no idea what function name we should use that won't add even more confusion :D
>>
>> Maybe folio_has_hwpoison(), and Miaohe may have some suggestion,
>> but leave it for later.
> 
> Will it be suitable to be named as something like folio_contain_hwpoisoned_page?

That sounds much better. "folio_has_hwpoison" is way to similar to 
"folio_test_has_hwpoisoned".

-- 
Cheers,

David / dhildenb