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SubjectRe: Infinite looping observed in __offline_pages
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On 08/23/2018 12:28 AM, Mike Kravetz wrote:
> On 08/22/2018 02:30 AM, Aneesh Kumar K.V wrote:
>> commit 2e9d754ac211f2af3731f15df3cd8cd070b4cc54
>> Author: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> Date: Tue Aug 21 14:17:55 2018 +0530
>>
>> mm/hugetlb: filter out hugetlb pages if HUGEPAGE migration is not supported.
>>
>> When scanning for movable pages, filter out Hugetlb pages if hugepage migration
>> is not supported. Without this we hit infinte loop in __offline pages where we
>> do
>> pfn = scan_movable_pages(start_pfn, end_pfn);
>> if (pfn) { /* We have movable pages */
>> ret = do_migrate_range(pfn, end_pfn);
>> goto repeat;
>> }
>>
>> We do support hugetlb migration ony if the hugetlb pages are at pmd level. Here
>
> I thought migration at pgd level was added for POWER? commit 94310cbcaa3c
> (mm/madvise: enable (soft|hard) offline of HugeTLB pages at PGD level).
> Only remember, because I did not fully understand the use case. :)
>

yes. We hit the issue on older distro kernels.

>> we just check for Kernel config. The gigantic page size check is done in
>> page_huge_active.
>>
>> Reported-by: Haren Myneni <haren@linux.vnet.ibm.com>
>> CC: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 4eb6e824a80c..f9bdea685cf4 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1338,7 +1338,8 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>> return pfn;
>> if (__PageMovable(page))
>> return pfn;
>> - if (PageHuge(page)) {
>> + if (IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION) &&
>> + PageHuge(page)) {
>
> How about using hugepage_migration_supported instead? It would automatically
> catch those non-migratable huge page sizes. Something like:
>


Will do that.

> if (PageHuge(page) &&
> hugepage_migration_supported(page_hstate(page))) {
>

-aneesh

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