linux-kernel - Re: Infinite looping observed in __offline

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Date:   Thu, 23 Aug 2018 08:31:34 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Haren Myneni <haren@...ux.vnet.ibm.com>
Cc:     n-horiguchi@...jp.nec.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, kamezawa.hiroyu@...fujitsu.com,
        mgorman@...e.de
Subject: Re: Infinite looping observed in __offline_pages

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@...ux.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@...ux.vnet.ibm.com>
>>      CC: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>>      Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.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