[PATCH v2] s390/mm: Allow hugepage migration for s390

[Gerald Schaefer <gerald.schaefer@linux.ibm.com>]

After hugetlbfs PTE_MARKER support for s390 introduced region-third
and segment table swap entries, it is possible to also allow hugepage
migration for s390.

This fixes the problem that hugetlbfs pages could not be allocated
from ZONE_MOVABLE memory, which is often used in combination with
memory hotplug. Therefore, without support for hugepage migration,
a large portion of system memory could be unavailable for hugetlbfs
page allocations.

Besides selecting ARCH_ENABLE_HUGEPAGE_MIGRATION, this only requires
definition of arch_hugetlb_migration_supported(), which can make use
of the existing arch_hugetlb_valid_size() function, similar to other
architectures.

Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
---
 arch/s390/Kconfig               |  1 +
 arch/s390/include/asm/hugetlb.h |  5 +++++
 arch/s390/mm/hugetlbpage.c      | 14 +++++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

---
Changes in v2:
- Use "#if IS_ENABLED()" instead of "#ifdef" in
  arch/s390/mm/hugetlbpage.c

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 612885228824..e3a704f423f3 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -83,6 +83,7 @@ config S390
 	select ALTERNATE_USER_ADDRESS_SPACE
 	select ARCH_32BIT_USTAT_F_TINODE
 	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
+	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
 	select ARCH_ENABLE_MEMORY_HOTPLUG if SPARSEMEM
 	select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
 	select ARCH_HAS_PMD_SOFTLEAVES if TRANSPARENT_HUGEPAGE
diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
index aea754b67c89..356a18a75d99 100644
--- a/arch/s390/include/asm/hugetlb.h
+++ b/arch/s390/include/asm/hugetlb.h
@@ -17,6 +17,11 @@
 
 #define hugepages_supported()	cpu_has_edat1()
 
+#ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
+bool arch_hugetlb_migration_supported(struct hstate *h);
+#define arch_hugetlb_migration_supported arch_hugetlb_migration_supported
+#endif
+
 #define __HAVE_ARCH_HUGE_SET_HUGE_PTE_AT
 void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
 		     pte_t *ptep, pte_t pte, unsigned long sz);
diff --git a/arch/s390/mm/hugetlbpage.c b/arch/s390/mm/hugetlbpage.c
index f84aa9265430..2c6e94888bd0 100644
--- a/arch/s390/mm/hugetlbpage.c
+++ b/arch/s390/mm/hugetlbpage.c
@@ -224,7 +224,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 	return (pte_t *) pmdp;
 }
 
-bool __init arch_hugetlb_valid_size(unsigned long size)
+static bool __hugetlb_valid_size(unsigned long size)
 {
 	if (cpu_has_edat1() && size == PMD_SIZE)
 		return true;
@@ -241,3 +241,15 @@ unsigned int __init arch_hugetlb_cma_order(void)
 
 	return 0;
 }
+
+bool __init arch_hugetlb_valid_size(unsigned long size)
+{
+	return __hugetlb_valid_size(size);
+}
+
+#if IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION)
+bool arch_hugetlb_migration_supported(struct hstate *h)
+{
+	return __hugetlb_valid_size(huge_page_size(h));
+}
+#endif
-- 
2.53.0