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

[Miaohe Lin <linmiaohe@huawei.com>]

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?

Thanks.
.