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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

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.

> 
>>               if (WARN_ON(folio_test_lru(folio)))
>>                   folio_isolate_lru(folio);
>>               if (folio_mapped(folio))
>> -                try_to_unmap(folio, TTU_IGNORE_MLOCK);
>> +                unmap_posioned_folio(folio, TTU_IGNORE_MLOCK);
>> +            continue;
>> +        }
>> +
>> +        if (folio_test_hugetlb(folio)) {
>> +            isolate_hugetlb(folio, &source);
>>               continue;
>>           }
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> 

Thanks.