linux-kernel - Re: Infinite looping observed in __offline

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Message-ID: <54c72a22-a921-fc64-460d-f66985d0df4e@oracle.com>
Date:   Wed, 22 Aug 2018 11:58:02 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.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 08/22/2018 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. :)

>     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:

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

-- 
Mike Kravetz

>  				if (page_huge_active(page))
>  					return pfn;
>  				else
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 15ea511fb41c..a3f81e18c882 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7649,6 +7649,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  		 * handle each tail page individually in migration.
>  		 */
>  		if (PageHuge(page)) {
> +
> +			if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION))
> +				goto unmovable;
> +
>  			iter = round_up(iter + 1, 1<<compound_order(page)) - 1;
>  			continue;
>  		}
>