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

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

On 2024/8/22 14:52, Miaohe Lin wrote:
> On 2024/8/17 16:49, 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
> 
> It should be commit e591ef7d96d6 ("mm,hwpoison,hugetlb,memory_hotplug: hotremove memory section
> with hwpoisoned hugepage")? Above "section with hwpoisoned")" is duplicated.
> 
> Also s/be clear/be cleared/ ?

Acked, thanks for carefully review.

> 
>> 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))) {
>>   			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);
> 
> While you're here, should we pr_warn "failed to isolate pfn xx" for hugetlb folios too as
> we already done for raw pages and thp folios?

We will unify folio isolation in final patch, which will print warn for 
hugetlb folio when failed to isolate, so no need to add here.
> 
> Thanks.
> .