In kubernetes 1.9, the node level memory is from root cgroup:
rootStats, networkStats, err := sp.provider.GetCgroupStats("/", updateStats)

While I found the node level memory from "/proc/meminfo" is different:

cat /proc/meminfo
MemTotal: 263774064 kB
MemFree: 59887272 kB
MemAvailable: 221831940 kB
Buffers: 1097668 kB
Cached: 154110176 kB
SwapCached: 0 kB
Active: 79424372 kB
Inactive: 98926152 kB
Active(anon): 23219964 kB
Inactive(anon): 171352 kB
Active(file): 56204408 kB
Inactive(file): 98754800 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 219692 kB
Writeback: 0 kB
AnonPages: 23143444 kB
Mapped: 2724656 kB
Shmem: 248384 kB
Slab: 11127012 kB
SReclaimable: 7229012 kB
SUnreclaim: 3898000 kB
KernelStack: 64432 kB
PageTables: 101444 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 131887032 kB
Committed_AS: 63167748 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 1520832 kB
VmallocChunk: 34223804980 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 15480156 kB
DirectMap2M: 202510336 kB
DirectMap1G: 52428800 kB

the node level memory used:
used = MemTotal - MemFree = 263774064 kB - 59887272 kB = 203886792KB
the real used:
real used = MemTotal - MemFree - （Buffers + Cached - Shmem）
= 263774064 kB - 59887272 kB - （1097668 kB + 154110176 kB - 248384 kB）
= 48927332kB

while from root cgroup:

cat /sys/fs/cgroup/memory/memory.usage_in_bytes
183140081664
cat /sys/fs/cgroup/memory/memory.stat
cache 39511924736
rss 267431936
rss_huge 0
mapped_file 424710144
swap 0
pgpgin 18514489
pgpgout 8802732
pgfault 12272911
pgmajfault 188
inactive_anon 651264
active_anon 268210176
inactive_file 33488736256
active_file 6021758976
unevictable 0
hierarchical_memory_limit 9223372036854775807
hierarchical_memsw_limit 9223372036854775807
total_cache 158941466624
total_rss 24187408384
total_rss_huge 0
total_mapped_file 1903247360
total_swap 0
total_pgpgin 5077787329
total_pgpgout 5033078131
total_pgfault 12592699800
total_pgmajfault 85677
total_inactive_anon 175456256
total_active_anon 24265732096
total_inactive_file 101087215616
total_active_file 57599930368
total_unevictable 0

the node level memory used:
used = memory.usage_in_bytes = 183140081664 = 178847736kB
the real used:
real used = memory.usage_in_bytes - total_inactive_file
= 183140081664 - 101087215616
= 82052866048
= 80129752kB

the two real used values is very different. Also, we used the same total value, so the "available" memory is also very different. 
This also have an effect on eviction in kubelet, shall we use the "/proc/meminfo"? for this may be more correct.