[PATCH] memblock: uniformly initialize all reserved pages to MIGRATE_MOVABLE

[Hua Su <suhua.tanke@gmail.com>]

Currently when CONFIG_DEFERRED_STRUCT_PAGE_INIT is not set, the reserved
pages are initialized to MIGRATE_MOVABLE by default in memmap_init.

Reserved memory mainly store the metadata of struct page. When
HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=Y and hugepages are allocated,
the HVO will remap the vmemmap virtual address range to the page which
vmemmap_reuse is mapped to. The pages previously mapping the range will
be freed to the buddy system.

Before this patch:
when CONFIG_DEFERRED_STRUCT_PAGE_INIT is not set, the freed memory was
placed on the Movable list;
When CONFIG_DEFERRED_STRUCT_PAGE_INIT=Y, the freed memory was placed on
the Unmovable list.

After this patch, the freed memory is placed on the Movable list
regardless of whether CONFIG_DEFERRED_STRUCT_PAGE_INIT is set.

Eg:
Tested on a virtual machine(1000GB):
Intel(R) Xeon(R) Platinum 8358P CPU

After vm start:
echo 500000 > /proc/sys/vm/nr_hugepages
cat /proc/meminfo | grep -i huge
HugePages_Total:   500000
HugePages_Free:    500000
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:        1024000000 kB

cat /proc/pagetypeinfo
before：
Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
…
Node    0, zone   Normal, type    Unmovable     51      2      1     28     53     35     35     43     40     69   3852
Node    0, zone   Normal, type      Movable   6485   4610    666    202    200    185    208     87     54      2    240
Node    0, zone   Normal, type  Reclaimable      2      2      1     23     13      1      2      1      0      1      0
Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
Unmovable ≈ 15GB

after：
Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
…
Node    0, zone   Normal, type    Unmovable      0      1      1      0      0      0      0      1      1      1      0
Node    0, zone   Normal, type      Movable   1563   4107   1119    189    256    368    286    132    109      4   3841
Node    0, zone   Normal, type  Reclaimable      2      2      1     23     13      1      2      1      0      1      0
Node    0, zone   Normal, type   HighAtomic      0      0      0      0      0      0      0      0      0      0      0
Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0

Signed-off-by: Hua Su <suhua.tanke@gmail.com>
---
 mm/mm_init.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 4ba5607aaf19..6dbf2df23eee 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -722,6 +722,10 @@ static void __meminit init_reserved_page(unsigned long pfn, int nid)
 		if (zone_spans_pfn(zone, pfn))
 			break;
 	}
+
+	if (pageblock_aligned(pfn))
+		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_MOVABLE);
+
 	__init_single_page(pfn_to_page(pfn), pfn, zid, nid);
 }
 #else
-- 
2.34.1