How does the 4G memory become 2G

4G memory becomes 2G-general Linux technology-Linux technology and application information. The following is a detailed description. A linux machine is a PAE kernel and can only be pinged but cannot be telnet.
After restarting, you can log on, but the memory is changed to 2 GB, as shown below:
[Root @ SCMMSC3_02 log] # more/proc/meminfo
MemTotal: 2070060 kB
MemFree: 51696 kB
Buffers': 8440 kB
Cached: 1659756 kB
SwapCached: 0 kB
Active: 957968 kB
Inactive: 960476 kB
HighTotal: 1173944 kB
HighFree: 1732 kB
LowTotal: 896116 kB
LowFree: 49964 kB
SwapTotal: 8385760 kB
SwapFree: 8385668 kB
Dirty: 205752 kB
Writeback: 48 kB
AnonPages: 250348 kB
Mapped: 83932 kB
Slab: 46452 kB
PageTables: 4608 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 9420788 kB
Committed_AS: 1585968 kB
VmallocTotal: 116728 kB
VmallocUsed: 7496 kB
VmallocChunk: 109112 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 kB

[Root @ SCMMSC3_02 log] # vmstat 2 10
Procs ----------- memory ---------- --- swap -- ----- io ---- system -- ----- cpu ------
R B swpd free buff cache si so bi bo in cs us sy id wa st
0 0 92 53080 8228 1659048 0 0 679 194 967 2 5 89 4 0
1 0 92 51716 8244 1661008 0 0 64 4618 2 2 95 0 0
2 0 92 61664 8048 1649820 0 0 0 16 4329 10 18 71 1 0
1 0 92 60424 8064 1651540 0 0 2332 4587 6457 10 7 81 2 0
1 1 92 51392 8120 1661144 0 0 4892 5055 5496 3 5 85 8 0
0 0 92 54728 8240 1658044 0 0 558 3128 4712 4 7 82 8 0
1 0 92 53116 8248 1659660 0 0 164 4264 2 4 93 0 0
0 0 92 54196 8268 1658240 0 0 0 40 4265 5 13 81 0 0
1 0 92 53080 8276 1659896 0 0 0 2110 4438 2 2 95 2 0
0 0 92 54080 8296 1658712 0 0 98 4439 5657 1 2 97 1 0
System log: Mar 15 15:38:23 SCMMSC3_02 kernel: Memory: 2067480 k/2093056 k available (2040 k kernel code, 22732 k reserved, 842 k data, 232 k init, 1173944 k highmem)



At the same time, the system log does not report an error, but only reports the following:
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8900000-b89fffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: b8d00000-b8dfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 2
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:25 SCMMSC3_02 hpiod: 1.6.7 accepting connections at 2208...
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8900000-b89fffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: b8d00000-b8dfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: 3000-3fff
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8000000-b88fffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: 3000-3fff
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8000000-b89fffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: b8d00000-b8dfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 3
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: 2000-2fff
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8a00000-b8bfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: b8c00000-b8cfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: 2000-3fff
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: b8000000-b8cfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: b8d00000-b8dfffff
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:25 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:25 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:26 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:26 SCMMSC3_02 kernel: IO window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: MEM window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PREFETCH window: disabled.
Mar 15 15:38:26 SCMMSC3_02 kernel: PCI: Bridge:. 0
Mar 15 15:38:26 SCMMSC3_02 kernel: IO window: disabled.

Why does the memory decrease? What does the last log mean? Thank you very much!