On 08/23/2018 12:28 AM, Mike Kravetz wrote:

On 08/22/2018 02:30 AM, Aneesh Kumar K.V wrote:

quoted

commit 2e9d754ac211f2af3731f15df3cd8cd070b4cc54
Author: Aneesh Kumar K.V [off-list ref]
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.

quoted

     we just check for Kernel config. The gigantic page size check is done in
     page_huge_active.
     
     Reported-by: Haren Myneni [off-list ref]
     CC: Naoya Horiguchi [off-list ref]
     Signed-off-by: Aneesh Kumar K.V [off-list ref]

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