我在 AWS 上运行了一个 t2.medium 实例CentOS 7 AMI我注意到它top基本上free报告了 3.45GiB 的总内存。如果我使用 AWS Linux 启动实例（我想我也尝试了 RedHat 实例），它会报告大约 4GiB 的内存。在网上浏览，我找不到其他人说为什么会这样。有谁知道为什么他们报告不同，或者这是否是一个可以修复的问题？
CentOS：
KiB Mem : 3619008 total, 1096408 free, 1218216 used, 1304384 buff/cache
AWS Linux：
Mem: 4049884k total, 459488k used, 3590396k free, 11440k buffers
编辑
我还启动了具有 1GiB RAM 的 RHEL：
KiB Mem : 1015472 total, 620588 free, 73452 used, 321432 buff/cache
所以现在，虽然操作系统接近相同，但报告的细节却不同，我认为这个版本的 AMI 中存在一些错误？
编辑2
cat /proc/meminfokdump关闭时 的输出：
MemTotal: 3783872 kB MemFree: 2682052 kB MemAvailable: 2799084 kB Buffers: 1328 kB Cached: 301760 kB SwapCached: 0 kB Active: 822816 kB Inactive: 153564 kB Active(anon): 676708 kB Inactive(anon): 25668 kB Active(file): 146108 kB Inactive(file): 127896 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 4194300 kB SwapFree: 4194300 kB Dirty: 292 kB Writeback: 0 kB AnonPages: 673292 kB Mapped: 47560 kB Shmem: 29084 kB Slab: 46348 kB SReclaimable: 23912 kB SUnreclaim: 22436 kB KernelStack: 3648 kB PageTables: 25784 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 6086236 kB Committed_AS: 1746036 kB VmallocTotal: 34359738367 kB VmallocUsed: 16640 kB VmallocChunk: 34359717628 kB HardwareCorrupted: 0 kB AnonHugePages: 147456 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 67584 kB DirectMap2M: 4126720 kB
编辑3
我已经关闭了 Kdump 并回收了一点空间但仍然缺少约 200MB。
dmesg输出：
[ 0.000000] Initializing cgroup subsys cpuset [ 0.000000] Initializing cgroup subsys cpu [ 0.000000] Initializing cgroup subsys cpuacct [ 0.000000] Linux version 3.10.0-327.10.1.el7.x86_64 ([email protected]) (gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC) ) #1 SMP Tue Feb 16 17:03:50 UTC 2016 [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.10.0-327.10.1.el7.x86_64 root=UUID=dd8f0afe-5a00-40ff-b538-5fa0a351cdba ro console=tty0 console=ttyS0,115200 [ 0.000000] e820: BIOS-provided physical RAM map: [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009dfff] usable ... [ 0.000000] NX (Execute Disable) protection: active [ 0.000000] SMBIOS 2.4 present. [ 0.000000] DMI: Xen HVM domU, BIOS 4.2.amazon 12/07/2015 [ 0.000000] Hypervisor detected: Xen HVM [ 0.000000] Xen version 4.2. [ 0.000000] Xen Platform PCI: I/O protocol version 1 [ 0.000000] Netfront and the Xen platform PCI driver have been compiled for this kernel: unplug emulated NICs. [ 0.000000] Blkfront and the Xen platform PCI driver have been compiled for this kernel: unplug emulated disks. You might have to change the root device from /dev/hd[a-d] to /dev/xvd[a-d] in your root= kernel command line option [ 0.000000] HVMOP_pagetable_dying not supported [ 0.000000] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved [ 0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable [ 0.000000] AGP: No AGP bridge found [ 0.000000] e820: last_pfn = 0x110000 max_arch_pfn = 0x400000000 [ 0.000000] MTRR default type: write-back [ 0.000000] MTRR fixed ranges enabled: [ 0.000000] 00000-9FFFF write-back [ 0.000000] A0000-BFFFF write-combining [ 0.000000] C0000-FFFFF write-back [ 0.000000] MTRR variable ranges enabled: [ 0.000000] 0 base 0000F0000000 mask 3FFFF8000000 uncatchable ... [ 0.000000] 2 disabled ... [ 0.000000] 7 disabled [ 0.000000] x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106 [ 0.000000] e820: last_pfn = 0xf0000 max_arch_pfn = 0x400000000 [ 0.000000] found SMP MP-table at [mem 0x000fbba0-0x000fbbaf] mapped at [ffff8800000fbba0] [ 0.000000] Base memory trampoline at [ffff880000098000] 98000 size 24576 [ 0.000000] init_memory_mapping: [mem 0x00000000-0x000fffff] [ 0.000000] [mem 0x00000000-0x000fffff] page 4k [ 0.000000] BRK [0x01f33000, 0x01f33fff] PGTABLE ... [ 0.000000] init_memory_mapping: [mem 0x10fe00000-0x10fffffff] [ 0.000000] [mem 0x10fe00000-0x10fffffff] page 2M [ 0.000000] BRK [0x01f36000, 0x01f36fff] PGTABLE [ 0.000000] init_memory_mapping: [mem 0x10c000000-0x10fdfffff] [ 0.000000] [mem 0x10c000000-0x10fdfffff] page 2M [ 0.000000] init_memory_mapping: [mem 0x100000000-0x10bffffff] [ 0.000000] [mem 0x100000000-0x10bffffff] page 2M [ 0.000000] init_memory_mapping: [mem 0x00100000-0xefffffff] [ 0.000000] [mem 0x00100000-0x001fffff] page 4k [ 0.000000] [mem 0x00200000-0xefffffff] page 2M [ 0.000000] RAMDISK: [mem 0x33a7c000-0x35d35fff] [ 0.000000] ACPI: RSDP 00000000000ea020 00024 (v02 Xen) [ 0.000000] ACPI: XSDT 00000000fc00f5a0 00054 (v01 Xen HVM 00000000 HVML 00000000) ... [ 0.000000] ACPI: SSDT 00000000fc00f560 00031 (v02 Xen HVM 00000000 INTL 20090123) [ 0.000000] ACPI: Local APIC address 0xfee00000 [ 0.000000] No NUMA configuration found [ 0.000000] Faking a node at [mem 0x0000000000000000-0x000000010fffffff] [ 0.000000] Initmem setup node 0 [mem 0x00000000-0x10fffffff] [ 0.000000] NODE_DATA [mem 0x10ffd6000-0x10fffcfff] [ 0.000000] [ffffea0000000000-ffffea00043fffff] PMD -> [ffff88010b600000-ffff88010f5fffff] on node 0 [ 0.000000] Zone ranges: [ 0.000000] DMA [mem 0x00001000-0x00ffffff] [ 0.000000] DMA32 [mem 0x01000000-0xffffffff] [ 0.000000] Normal [mem 0x100000000-0x10fffffff] [ 0.000000] Movable zone start for each node [ 0.000000] Early memory node ranges [ 0.000000] node 0: [mem 0x00001000-0x0009dfff] ... [ 0.000000] On node 0 totalpages: 1048477 [ 0.000000] DMA zone: 64 pages used for memmap [ 0.000000] DMA zone: 21 pages reserved [ 0.000000] DMA zone: 3997 pages, LIFO batch:0 [ 0.000000] DMA32 zone: 15296 pages used for memmap [ 0.000000] DMA32 zone: 978944 pages, LIFO batch:31 [ 0.000000] Normal zone: 1024 pages used for memmap [ 0.000000] Normal zone: 65536 pages, LIFO batch:15 [ 0.000000] ACPI: PM-Timer IO Port: 0xb008 [ 0.000000] ACPI: Local APIC address 0xfee00000 [ 0.000000] ACPI: LAPIC (acpi_id[0x00] lapic_id[0x00] enabled) ... [ 0.000000] ACPI: LAPIC (acpi_id[0x0e] lapic_id[0x00] disabled) [ 0.000000] ACPI: IOAPIC (id[0x01] address[0xfec00000] gsi_base[0]) [ 0.000000] IOAPIC[0]: apic_id 1, version 17, address 0xfec00000, GSI 0-47 [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl) ... [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 11 global_irq 11 low level) [ 0.000000] ACPI: IRQ0 used by override. ... [ 0.000000] ACPI: IRQ11 used by override. [ 0.000000] Using ACPI (MADT) for SMP configuration information [ 0.000000] ACPI: HPET id: 0x8086a201 base: 0xfed00000 [ 0.000000] smpboot: Allowing 15 CPUs, 13 hotplug CPUs [ 0.000000] PM: Registered nosave memory: [mem 0x0009e000-0x0009ffff] ... [ 0.000000] PM: Registered nosave memory: [mem 0xfc000000-0xffffffff] [ 0.000000] e820: [mem 0xf0000000-0xfbffffff] available for PCI devices [ 0.000000] Booting paravirtualized kernel on Xen HVM [ 0.000000] setup_percpu: NR_CPUS:5120 nr_cpumask_bits:15 nr_cpu_ids:15 nr_node_ids:1 [ 0.000000] PERCPU: Embedded 31 pages/cpu @ffff88010fc00000 s87168 r8192 d31616 u131072 [ 0.000000] pcpu-alloc: s87168 r8192 d31616 u131072 alloc=1*2097152 [ 0.000000] pcpu-alloc: [0] 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 -- [ 0.000000] Built 1 zonelists in Node order, mobility grouping on. Total pages: 1032072 [ 0.000000] Policy zone: Normal [ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.10.0-327.10.1.el7.x86_64 root=UUID=dd8f0afe-5a00-40ff-b538-5fa0a351cdba ro console=tty0 console=ttyS0,115200 [ 0.000000] PID hash table entries: 4096 (order: 3, 32768 bytes) [ 0.000000] x86/fpu: xstate_offset[2]: 0240, xstate_sizes[2]: 0100 [ 0.000000] xsave: enabled xstate_bv 0x7, cntxt size 0x340 [ 0.000000] AGP: Checking aperture... [ 0.000000] AGP: No AGP bridge found [ 0.000000] Memory: 4008808k/4456448k available (6440k kernel code, 262540k absent, 185100k reserved, 4266k data, 1620k init) [ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=15, Nodes=1 [ 0.000000] Hierarchical RCU implementation. [ 0.000000] RCU restricting CPUs from NR_CPUS=5120 to nr_cpu_ids=15. [ 0.000000] Offload RCU callbacks from all CPUs [ 0.000000] Offload RCU callbacks from CPUs: 0-14. [ 0.000000] NR_IRQS:327936 nr_irqs:952 0 [ 0.000000] xen:events: Xen HVM callback vector for event delivery is enabled [ 0.000000] Console: colour VGA+ 80x25 [ 0.000000] console [tty0] enabled [ 0.000000] Cannot get hvm parameter CONSOLE_EVTCHN (18): -22! [ 0.000000] console [ttyS0] enabled [ 0.000000] allocated 16777216 bytes of page_cgroup [ 0.000000] please try 'cgroup_disable=memory' option if you don't want memory cgroups [ 0.000000] hpet clockevent registered [ 0.000000] tsc: Detected 2500.056 MHz processor [ 0.005000] Calibrating delay loop (skipped), value calculated using timer frequency.. 5000.11 BogoMIPS (lpj=2500056) [ 0.013004] pid_max: default: 32768 minimum: 301 [ 0.017040] Security Framework initialized [ 0.020007] SELinux: Initializing. [ 0.023011] SELinux: Starting in permissive mode [ 0.024124] Dentry cache hash table entries: 524288 (order: 10, 4194304 bytes) [ 0.030768] Inode-cache hash table entries: 262144 (order: 9, 2097152 bytes) [ 0.035392] Mount-cache hash table entries: 4096 [ 0.039203] Initializing cgroup subsys memory ... [ 0.060004] Initializing cgroup subsys hugetlb [ 0.064066] CPU: Physical Processor ID: 0 [ 0.067002] CPU: Processor Core ID: 0 [ 0.071304] mce: CPU supports 2 MCE banks [ 0.074023] Last level iTLB entries: 4KB 512, 2MB 0, 4MB 0 Last level dTLB entries: 4KB 512, 2MB 0, 4MB 0 tlb_flushall_shift: 6 [ 0.084252] Freeing SMP alternatives: 28k freed [ 0.091062] ACPI: Core revision 20130517 [ 0.097913] ACPI: All ACPI Tables successfully acquired [ 0.102004] ftrace: allocating 24584 entries in 97 pages [ 0.133003] Switched APIC routing to physical flat. [ 0.139406] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=0 pin2=0 [ 0.154095] smpboot: CPU0: Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz (fam: 06, model: 3e, stepping: 04) [ 0.162007] Xen: using vcpuop timer interface [ 0.162014] installing Xen timer for CPU 0 [ 0.166087] cpu 0 spinlock event irq 53 [ 0.167041] Performance Events: unsupported p6 CPU model 62 no PMU driver, software events only. [ 0.171416] NMI watchdog: disabled (cpu0): hardware events not enabled [ 0.172074] installing Xen timer for CPU 1 [ 0.173068] smpboot: Booting Node 0, Processors #1cpu 1 spinlock event irq 59 [ 0.188029] Brought up 2 CPUs [ 0.189005] smpboot: Total of 2 processors activated (10000.22 BogoMIPS) [ 0.190596] devtmpfs: initialized [ 0.194990] EVM: security.selinux [ 0.199005] EVM: security.ima [ 0.201006] EVM: security.capability [ 0.205725] atomic64 test passed for x86-64 platform with CX8 and with SSE [ 0.210134] NET: Registered protocol family 16 [ 0.214116] ACPI: bus type PCI registered [ 0.218006] acpiphp: ACPI Hot Plug PCI Controller Driver version: 0.5 [ 0.222332] PCI: Using configuration type 1 for base access [ 0.227085] ACPI: Added _OSI(Module Device) [ 0.231006] ACPI: Added _OSI(Processor Device) [ 0.234005] ACPI: Added _OSI(3.0 _SCP Extensions) [ 0.238007] ACPI: Added _OSI(Processor Aggregator Device) [ 0.243367] ACPI: EC: Look up EC in DSDT [ 0.246343] ACPI: Interpreter enabled [ 0.250016] ACPI Exception: AE_NOT_FOUND, While evaluating Sleep State [\_S1_] (20130517/hwxface-571) [ 0.257007] ACPI Exception: AE_NOT_FOUND, While evaluating Sleep State [\_S2_] (20130517/hwxface-571) [ 0.265014] ACPI: (supports S0 S3 S4 S5) [ 0.268005] ACPI: Using IOAPIC for interrupt routing [ 0.272041] PCI: Using host bridge windows from ACPI; if necessary, use "pci=nocrs" and report a bug [ 0.345050] ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff]) [ 0.346011] acpi PNP0A03:00: _OSC: OS supports [ASPM ClockPM Segments MSI] [ 0.347015] acpi PNP0A03:00: _OSC failed (AE_NOT_FOUND); disabling ASPM [ 0.348081] acpi PNP0A03:00: fail to add MMCONFIG information, can't access extended PCI configuration space under this bridge. [ 0.349808] acpiphp: Slot [0] registered ... [ 0.378310] acpiphp: Slot [31] registered [ 0.379309] PCI host bridge to bus 0000:00 [ 0.380023] pci_bus 0000:00: root bus resource [bus 00-ff] ... [ 0.390382] pci 0000:00:01.1: reg 0x20: [io 0xc100-0xc10f] [ 0.390920] pci 0000:00:01.1: legacy IDE quirk: reg 0x10: [io 0x01f0-0x01f7] ... [ 0.394697] pci 0000:00:01.3: [8086:7113] type 00 class 0x068000 [ 0.394733] * Found PM-Timer Bug on the chipset. Due to workarounds for a bug, * this clock source is slow. Consider trying other clock sources [ 0.396352] pci 0000:00:01.3: quirk: [io 0xb000-0xb03f] claimed by PIIX4 ACPI [ 0.397918] pci 0000:00:02.0: [1013:00b8] type 00 class 0x030000 [ 0.398172] pci 0000:00:02.0: reg 0x10: [mem 0xf0000000-0xf1ffffff pref] [ 0.398431] pci 0000:00:02.0: reg 0x14: [mem 0xf3000000-0xf3000fff] [ 0.400291] pci 0000:00:03.0: [5853:0001] type 00 class 0xff8000 [ 0.400632] pci 0000:00:03.0: reg 0x10: [io 0xc000-0xc0ff] [ 0.400898] pci 0000:00:03.0: reg 0x14: [mem 0xf2000000-0xf2ffffff pref] [ 0.403567] ACPI: PCI Interrupt Link [LNKA] (IRQs *5 10 11) ... [ 0.414208] ACPI: PCI Interrupt Link [LNKD] (IRQs *5 10 11) [ 0.435706] ACPI: Enabled 2 GPEs in block 00 to 0F [ 0.436083] xen:balloon: Initialising balloon driver [ 0.441026] xen_balloon: Initialising balloon driver [ 0.445070] vgaarb: device added: PCI:0000:00:02.0,decodes=io+mem,owns=io+mem,locks=none [ 0.452007] vgaarb: loaded [ 0.454004] vgaarb: bridge control possible 0000:00:02.0 [ 0.465074] SCSI subsystem initialized [ 0.469047] ACPI: bus type USB registered [ 0.480707] usbcore: registered new interface driver usbfs [ 0.485015] usbcore: registered new interface driver hub [ 0.496039] usbcore: registered new device driver usb [ 0.508075] PCI: Using ACPI for IRQ routing [ 0.512007] PCI: pci_cache_line_size set to 64 bytes [ 0.512427] e820: reserve RAM buffer [mem 0x0009e000-0x0009ffff] [ 0.512543] NetLabel: Initializing [ 0.516005] NetLabel: domain hash size = 128 [ 0.520004] NetLabel: protocols = UNLABELED CIPSOv4 [ 0.534049] NetLabel: unlabeled traffic allowed by default [ 0.535076] HPET: 3 timers in total, 0 timers will be used for per-cpu timer [ 0.536042] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0 [ 0.539006] hpet0: 3 comparators, 64-bit 62.500000 MHz counter [ 0.775037] Switching to clocksource xen [ 0.780573] pnp: PnP ACPI init [ 0.783587] ACPI: bus type PNP registered [ 0.787272] system 00:00: [mem 0x00000000-0x0009ffff] could not be reserved [ 0.792532] system 00:00: Plug and Play ACPI device, IDs PNP0c02 (active) [ 0.792586] pnp 00:01: Plug and Play ACPI device, IDs PNP0103 (active) [ 0.792620] system 00:02: [io 0x08a0-0x08a3] has been reserved ... [ 0.802087] system 00:02: [io 0x04d0-0x04d1] has been reserved [ 0.806860] system 00:02: Plug and Play ACPI device, IDs PNP0c02 (active) [ 0.806884] pnp 00:03: [dma 4] [ 0.806920] pnp 00:03: Plug and Play ACPI device, IDs PNP0200 (active) [ 0.806942] xen: --> pirq=16 -> irq=8 (gsi=8) [ 0.806955] pnp 00:04: Plug and Play ACPI device, IDs PNP0b00 (active) ... [ 0.806993] xen: --> pirq=17 -> irq=12 (gsi=12) [ 0.807002] pnp 00:06: Plug and Play ACPI device, IDs PNP0f13 (active) [ 0.807019] xen: --> pirq=18 -> irq=1 (gsi=1) [ 0.807032] pnp 00:07: Plug and Play ACPI device, IDs PNP0303 PNP030b (active) [ 0.807048] xen: --> pirq=19 -> irq=6 (gsi=6) [ 0.807051] pnp 00:08: [dma 2] [ 0.807069] pnp 00:08: Plug and Play ACPI device, IDs PNP0700 (active) [ 0.807095] xen: --> pirq=20 -> irq=4 (gsi=4) [ 0.807108] pnp 00:09: Plug and Play ACPI device, IDs PNP0501 (active) [ 0.807142] system 00:0a: [io 0x10c0-0x1141] has been reserved [ 0.811864] system 00:0a: [io 0xb044-0xb047] has been reserved [ 0.816579] system 00:0a: Plug and Play ACPI device, IDs PNP0c02 (active) [ 0.835070] pnp: PnP ACPI: found 11 devices [ 0.838578] ACPI: bus type PNP unregistered [ 0.849503] pci_bus 0000:00: resource 4 [io 0x0000-0x0cf7] ... [ 0.849507] pci_bus 0000:00: resource 6 [mem 0x000a0000-0x000bffff] ... [ 0.849541] NET: Registered protocol family 2 [ 0.854104] TCP established hash table entries: 32768 (order: 6, 262144 bytes) [ 0.860212] TCP bind hash table entries: 32768 (order: 7, 524288 bytes) [ 0.865152] TCP: Hash tables configured (established 32768 bind 32768) [ 0.870016] TCP: reno registered [ 0.873214] UDP hash table entries: 2048 (order: 4, 65536 bytes) [ 0.877886] UDP-Lite hash table entries: 2048 (order: 4, 65536 bytes) [ 0.882952] NET: Registered protocol family 1 [ 0.886554] pci 0000:00:00.0: Limiting direct PCI/PCI transfers [ 0.891169] pci 0000:00:01.0: PIIX3: Enabling Passive Release [ 0.895949] pci 0000:00:01.0: Activating ISA DMA hang workarounds [ 0.900811] pci 0000:00:02.0: Boot video device [ 0.900878] PCI: CLS 0 bytes, default 64 [ 0.900930] Unpacking initramfs... [ 1.370039] Freeing initrd memory: 35560k freed [ 1.382776] PCI-DMA: Using software bounce buffering for IO (SWIOTLB) [ 1.387812] software IO TLB [mem 0xec000000-0xf0000000] (64MB) mapped at [ffff8800ec000000-ffff8800efffffff] [ 1.395560] RAPL PMU detected, API unit is 2^-32 Joules, 3 fixed counters 163840 ms ovfl timer [ 1.402348] hw unit of domain pp0-core 2^-16 Joules [ 1.406346] hw unit of domain package 2^-16 Joules [ 1.410208] hw unit of domain dram 2^-16 Joules [ 1.414438] microcode: CPU0 sig=0x306e4, pf=0x1, revision=0x416 ... [ 1.423672] microcode: Microcode Update Driver: v2.00 <[email protected]>, Peter Oruba [ 1.430934] sha1_ssse3: Using AVX optimized SHA-1 implementation [ 1.435656] sha256_ssse3: Using AVX optimized SHA-256 implementation [ 1.440884] futex hash table entries: 4096 (order: 6, 262144 bytes) [ 1.445953] Initialise system trusted keyring [ 1.449714] audit: initializing netlink socket (disabled) [ 1.454053] type=2000 audit(1460748590.383:1): initialized [ 1.479381] HugeTLB registered 2 MB page size, pre-allocated 0 pages [ 1.485298] zpool: loaded [ 1.488040] zbud: loaded [ 1.490923] VFS: Disk quotas dquot_6.5.2 [ 1.494507] Dquot-cache hash table entries: 512 (order 0, 4096 bytes) [ 1.499951] msgmni has been set to 7387 [ 1.503432] Key type big_key registered [ 1.506711] SELinux: Registering netfilter hooks [ 1.507730] NET: Registered protocol family 38 [ 1.511538] Key type asymmetric registered [ 1.515054] Asymmetric key parser 'x509' registered [ 1.519027] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 251) [ 1.525577] io scheduler noop registered [ 1.529021] io scheduler deadline registered (default) [ 1.533344] io scheduler cfq registered [ 1.537151] pci_hotplug: PCI Hot Plug PCI Core version: 0.5 [ 1.541386] pciehp: PCI Express Hot Plug Controller Driver version: 0.4 [ 1.546422] intel_idle: does not run on family 6 model 62 [ 1.546499] input: Power Button as /devices/LNXSYSTM:00/LNXPWRBN:00/input/input0 [ 1.552505] ACPI: Power Button [PWRF] [ 1.556208] input: Sleep Button as /devices/LNXSYSTM:00/LNXSLPBN:00/input/input1 [ 1.562654] ACPI: Sleep Button [SLPF] [ 1.566048] GHES: HEST is not enabled! [ 1.569688] xen: --> pirq=21 -> irq=28 (gsi=28) [ 1.569765] xen:grant_table: Grant tables using version 1 layout [ 1.574524] Grant table initialized [ 1.577755] Cannot get hvm parameter CONSOLE_EVTCHN (18): -22! [ 1.582372] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled [ 1.614794] 00:09: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A [ 1.620038] Non-volatile memory driver v1.3 [ 1.623599] Linux agpgart interface v0.103 [ 1.627302] crash memory driver: version 1.1 [ 1.630956] rdac: device handler registered [ 1.634477] hp_sw: device handler registered [ 1.637974] emc: device handler registered [ 1.641456] alua: device handler registered [ 1.645089] libphy: Fixed MDIO Bus: probed [ 1.648698] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver [ 1.653541] ehci-pci: EHCI PCI platform driver [ 1.657751] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver [ 1.662445] ohci-pci: OHCI PCI platform driver [ 1.666172] uhci_hcd: USB Universal Host Controller Interface driver [ 1.671042] usbcore: registered new interface driver usbserial [ 1.675477] usbcore: registered new interface driver usbserial_generic [ 1.680211] usbserial: USB Serial support registered for generic [ 1.684936] i8042: PNP: PS/2 Controller [PNP0303:PS2K,PNP0f13:PS2M] at 0x60,0x64 irq 1,12 [ 1.693451] serio: i8042 KBD port at 0x60,0x64 irq 1 [ 1.697654] serio: i8042 AUX port at 0x60,0x64 irq 12 [ 1.701942] mousedev: PS/2 mouse device common for all mice [ 1.707169] input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input2 [ 1.714459] rtc_cmos 00:04: rtc core: registered rtc_cmos as rtc0 [ 1.720970] rtc_cmos 00:04: alarms up to one day, 114 bytes nvram, hpet irqs [ 1.726774] cpuidle: using governor menu [ 1.730197] hidraw: raw HID events driver (C) Jiri Kosina [ 1.734504] usbcore: registered new interface driver usbhid [ 1.738851] usbhid: USB HID core driver [ 1.742264] drop_monitor: Initializing network drop monitor service [ 1.747070] TCP: cubic registered [ 1.750203] Initializing XFRM netlink socket [ 1.753891] NET: Registered protocol family 10 [ 1.757968] NET: Registered protocol family 17 [ 1.762078] Loading compiled-in X.509 certificates [ 1.765952] Loaded X.509 cert 'CentOS Linux kpatch signing key: ea0413152cde1d98ebdca3fe6f0230904c9ef717' [ 1.773397] Loaded X.509 cert 'CentOS Linux Driver update signing key: 7f421ee0ab69461574bb358861dbe77762a4201b' [ 1.781437] Loaded X.509 cert 'CentOS Linux kernel signing key: 756354566b6c2e3c931c0a3bf44c8294fccbce3a' [ 1.806084] registered taskstats version 1 [ 1.811489] Key type trusted registered [ 1.816618] Key type encrypted registered [ 1.821587] IMA: No TPM chip found, activating TPM-bypass! [ 1.826295] xenbus_probe_frontend: Device with no driver: device/vfb/0 ... [ 1.852051] xenbus_probe_frontend: Device with no driver: device/vif/0 [ 1.857158] rtc_cmos 00:04: setting system clock to 2016-04-15 19:29:51 UTC (1460748591) [ 1.866113] Freeing unused kernel memory: 1620k freed [ 1.874542] systemd[1]: systemd 219 running in system mode. (+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN) [ 1.887720] systemd[1]: Detected virtualization xen. [ 1.891810] systemd[1]: Detected architecture x86-64. [ 1.896050] systemd[1]: Running in initial RAM disk. [ 1.904088] systemd[1]: No hostname configured. [ 1.907882] systemd[1]: Set hostname to <localhost>. [ 1.911832] systemd[1]: Initializing machine ID from random generator. [ 1.956032] systemd[1]: Reached target Local File Systems. [ 1.960872] systemd[1]: Starting Local File Systems. [ 1.967877] systemd[1]: Reached target Swap. [ 1.971511] systemd[1]: Starting Swap. [ 1.977704] systemd[1]: Reached target Timers. [ 1.981363] systemd[1]: Starting Timers. [ 1.987805] systemd[1]: Created slice -.slice. [ 1.991574] systemd[1]: Starting -.slice. [ 1.998610] systemd[1]: Listening on udev Control Socket. [ 2.002939] systemd[1]: Starting udev Control Socket. [ 2.010145] systemd[1]: Listening on udev Kernel Socket. [ 2.014478] systemd[1]: Starting udev Kernel Socket. [ 2.021584] systemd[1]: Listening on Journal Socket. [ 2.025579] systemd[1]: Starting Journal Socket. [ 2.029510] systemd[1]: Started Dispatch Password Requests to Console Directory Watch. [ 2.035921] systemd[1]: Starting Dispatch Password Requests to Console Directory Watch. [ 2.045313] systemd[1]: Reached target Paths. ... [ 2.091990] systemd[1]: Starting Journal Service... [ 2.099117] systemd[1]: Starting Create list of required static device nodes for the current kernel... [ 2.111135] systemd[1]: Starting dracut cmdline hook... [ 2.120901] systemd[1]: Reached target Sockets. [ 2.124667] systemd[1]: Starting Sockets. [ 2.131983] systemd[1]: Started Journal Service. [ 2.214968] RPC: Registered named UNIX socket transport module. [ 2.219794] RPC: Registered udp transport module. [ 2.223605] RPC: Registered tcp transport module. [ 2.227558] RPC: Registered tcp NFSv4.1 backchannel transport module. [ 2.396079] tsc: Refined TSC clocksource calibration: 2500.000 MHz [ 2.404145] FDC 0 is a S82078B [ 2.414902] libata version 3.00 loaded. [ 2.415783] ata_piix 0000:00:01.1: version 2.13 [ 2.416790] scsi host0: ata_piix [ 2.420209] scsi host1: ata_piix [ 2.424025] ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc100 irq 14 [ 2.429172] ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc108 irq 15 [ 2.441339] xen_netfront: Initialising Xen virtual ethernet driver [ 2.503105] blkfront: xvda: barrier or flush: disabled; persistent grants: disabled; indirect descriptors: enabled; [ 2.526726] xvda: xvda1 [ 2.538259] blkfront: xvdb: barrier or flush: disabled; persistent grants: disabled; indirect descriptors: enabled; [ 2.553835] xvdb: unknown partition table [ 2.561480] blkfront: xvdm: barrier or flush: disabled; persistent grants: disabled; indirect descriptors: enabled; [ 2.564125] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8042/serio1/input/input3 [ 2.580077] xvdm: unknown partition table [ 2.596005] blkfront: xvdl: barrier or flush: disabled; persistent grants: disabled; indirect descriptors: enabled; [ 2.606573] xvdl: unknown partition table [ 2.610467] Setting capacity to 8388608 [ 2.614016] xvdm: detected capacity change from 0 to 4294967296 [ 2.735355] SGI XFS with ACLs, security attributes, no debug enabled [ 2.742377] XFS (xvda1): Mounting V4 Filesystem [ 3.881703] XFS (xvda1): Ending clean mount [ 4.275374] systemd-journald[125]: Received SIGTERM from PID 1 (systemd). [ 4.380362] SELinux: Disabled at runtime. [ 4.384006] SELinux: Unregistering netfilter hooks [ 4.403113] type=1404 audit(1460748594.045:2): selinux=0 auid=4294967295 ses=4294967295 [ 4.429738] ip_tables: (C) 2000-2006 Netfilter Core Team [ 4.434250] systemd[1]: Inserted module 'ip_tables' [ 4.643894] Installing knfsd (copyright (C) 1996 [email protected]). [ 4.852747] systemd-journald[389]: Received request to flush runtime journal from PID 1 [ 4.980173] type=1305 audit(1460748594.622:3): audit_pid=432 old=0 auid=4294967295 ses=4294967295 res=1 [ 5.025952] piix4_smbus 0000:00:01.3: SMBus base address uninitialized - upgrade BIOS or use force_addr=0xaddr [ 5.044837] [drm] Initialized drm 1.1.0 20060810 [ 5.071499] input: PC Speaker as /devices/platform/pcspkr/input/input4 [ 5.090615] [TTM] Zone kernel: Available graphics memory: 1891936 kiB [ 5.095585] [TTM] Initializing pool allocator [ 5.101566] [TTM] Initializing DMA pool allocator [ 5.106805] [drm] fb mappable at 0xF0000000 [ 5.110834] [drm] vram aper at 0xF0000000 [ 5.110835] [drm] size 33554432 [ 5.110835] [drm] fb depth is 24 [ 5.110836] [drm] pitch is 3072 [ 5.123760] fbcon: cirrusdrmfb (fb0) is primary device [ 5.138883] ppdev: user-space parallel port driver [ 5.160861] Error: Driver 'pcspkr' is already registered, aborting... [ 5.175471] AES CTR mode by8 optimization enabled [ 5.178614] alg: No test for __gcm-aes-aesni (__driver-gcm-aes-aesni) [ 5.184269] alg: No test for crc32 (crc32-pclmul) [ 5.186337] Console: switching to colour frame buffer device 128x48 [ 5.256497] cirrus 0000:00:02.0: fb0: cirrusdrmfb frame buffer device [ 5.256498] cirrus 0000:00:02.0: registered panic notifier [ 5.256502] [drm] Initialized cirrus 1.0.0 20110418 for 0000:00:02.0 on minor 0 [ 5.279587] Adding 4194300k swap on /dev/xvdm. Priority:-1 extents:1 across:4194300k SSFS [ 6.678040] ISOFS: Unable to identify CD-ROM format.
答案1
也许您已经crashkernel在 CentOS 实例上启用了该功能。
它基本上会保留一部分内存，以便在主内核崩溃/死锁的情况下启动“崩溃内核”。
请显示输出以cat /proc/cmdline验证。
更新：至于“丢失”的另外 200 MB，看起来似乎/proc/meminfo是为 PCI 总线/设备保留的。以下行：
f0000000-fbffffff : PCI Bus 0000:00
包含 201326591 KB，或者大约 200 MB。
为什么该内存是为 CentOS7 AMI 保留的，而不是为 AWS Linux 保留的？
- 首先，两个 AMI 可以公开不同的虚拟化硬件平台。因此，预留的 PCI 空间可以不同
- 其次，AWS 提供两种 AMI 类型：HVM 和 PV。后者可以避免一些 PCI 重映射，从而获得更多可用内存。
更新：似乎dmesg证实了一些内存是为设备映射保留的。该行Memory: 4008808k显示比完整的 4 GB（4194304 KB）少 185496 KB
答案2
它看起来像一个带有 centos 的 32 位内核。