Linux内核的内存相关的信息主要有下面几个获取管道，这里我们主要讨论的是系统级别的，没具体到各个进程级别：
1. 内核启动时候，VM内存相关模块初始化信息，透过dmesg查看。
详细描述可参考这里
比如：
NUMA: Using 30 for the hash shift.
Bootmem setup node 0 0000000000000000-0000000340000000
Bootmem setup node 1 0000000340000000-0000000640000000
On node 0 totalpages: 3095549
DMA zone: 2613 pages, LIFO batch:0
DMA32 zone: 765896 pages, LIFO batch:31
Normal zone: 2327040 pages, LIFO batch:31
On node 1 totalpages: 3102720
Normal zone: 3102720 pages, LIFO batch:31
…
Memory: 24543920k/26214400k available (2547k kernel code, 612792k reserved, 1289k data, 208k init)
…
Total HugeTLB memory allocated, 0
…
2. /proc/meminfo。
每个字段的意思，可参考这里
比如：
$cat /proc/meminfo
MemTotal: 24545764 kB
MemFree: 957064 kB
Buffers: 1739164 kB
Cached: 10699300 kB
SwapCached: 3816 kB
Active: 17884180 kB
Inactive: 4479128 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 24545764 kB
LowFree: 957064 kB
SwapTotal: 6289320 kB
SwapFree: 5005124 kB
Dirty: 28 kB
Writeback: 0 kB
AnonPages: 9923908 kB
Mapped: 27068 kB
Slab: 1132452 kB
PageTables: 41560 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 18562200 kB
Committed_AS: 33474640 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 268160 kB
VmallocChunk: 34359470063 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 kB
3. sysrq-trigger的m键。
首先启用这个特性：
sudo sysctl kernel.sysrq=1
获取帮助：
echo h | sudo tee /proc/sysrq-trigger
SysRq : HELP : loglevel0-8 reBoot Crashdump tErm Full kIll thaw-filesystems(J) saK showMem Nice powerOff showPc unRaw Sync showTasks Unmount shoWcpus
获取内存信息：
echo m | sudo tee /proc/sysrq-trigger
SysRq : Show Memory
Mem-info:
Node 0 DMA per-cpu:
cpu 0 hot: high 0, batch 1 used:0
cpu 0 cold: high 0, batch 1 used:0
cpu 1 hot: high 0, batch 1 used:0
cpu 1 cold: high 0, batch 1 used:0
cpu 2 hot: high 0, batch 1 used:0
cpu 2 cold: high 0, batch 1 used:0
cpu 3 hot: high 0, batch 1 used:0
cpu 3 cold: high 0, batch 1 used:0
cpu 4 hot: high 0, batch 1 used:0
cpu 4 cold: high 0, batch 1 used:0
cpu 5 hot: high 0, batch 1 used:0
cpu 5 cold: high 0, batch 1 used:0
cpu 6 hot: high 0, batch 1 used:0
cpu 6 cold: high 0, batch 1 used:0
cpu 7 hot: high 0, batch 1 used:0
cpu 7 cold: high 0, batch 1 used:0
cpu 8 hot: high 0, batch 1 used:0
cpu 8 cold: high 0, batch 1 used:0
cpu 9 hot: high 0, batch 1 used:0
cpu 9 cold: high 0, batch 1 used:0
cpu 10 hot: high 0, batch 1 used:0
cpu 10 cold: high 0, batch 1 used:0
cpu 11 hot: high 0, batch 1 used:0
cpu 11 cold: high 0, batch 1 used:0
cpu 12 hot: high 0, batch 1 used:0
cpu 12 cold: high 0, batch 1 used:0
cpu 13 hot: high 0, batch 1 used:0
cpu 13 cold: high 0, batch 1 used:0
cpu 14 hot: high 0, batch 1 used:0
cpu 14 cold: high 0, batch 1 used:0
cpu 15 hot: high 0, batch 1 used:0
cpu 15 cold: high 0, batch 1 used:0
Node 0 DMA32 per-cpu:
cpu 0 hot: high 186, batch 31 used:70
cpu 0 cold: high 62, batch 15 used:59
cpu 1 hot: high 186, batch 31 used:24
cpu 1 cold: high 62, batch 15 used:13
cpu 2 hot: high 186, batch 31 used:7
cpu 2 cold: high 62, batch 15 used:11
cpu 3 hot: high 186, batch 31 used:19
cpu 3 cold: high 62, batch 15 used:54
cpu 4 hot: high 186, batch 31 used:0
cpu 4 cold: high 62, batch 15 used:0
cpu 5 hot: high 186, batch 31 used:0
cpu 5 cold: high 62, batch 15 used:0
cpu 6 hot: high 186, batch 31 used:0
cpu 6 cold: high 62, batch 15 used:0
cpu 7 hot: high 186, batch 31 used:0
cpu 7 cold: high 62, batch 15 used:0
cpu 8 hot: high 186, batch 31 used:16
cpu 8 cold: high 62, batch 15 used:50
cpu 9 hot: high 186, batch 31 used:23
cpu 9 cold: high 62, batch 15 used:2
cpu 10 hot: high 186, batch 31 used:40
cpu 10 cold: high 62, batch 15 used:41
cpu 11 hot: high 186, batch 31 used:157
cpu 11 cold: high 62, batch 15 used:5
cpu 12 hot: high 186, batch 31 used:0
cpu 12 cold: high 62, batch 15 used:0
cpu 13 hot: high 186, batch 31 used:0
cpu 13 cold: high 62, batch 15 used:0
cpu 14 hot: high 186, batch 31 used:0
cpu 14 cold: high 62, batch 15 used:0
cpu 15 hot: high 186, batch 31 used:0
cpu 15 cold: high 62, batch 15 used:0
Node 0 Normal per-cpu:
cpu 0 hot: high 186, batch 31 used:50
cpu 0 cold: high 62, batch 15 used:13
cpu 1 hot: high 186, batch 31 used:159
cpu 1 cold: high 62, batch 15 used:14
cpu 2 hot: high 186, batch 31 used:155
cpu 2 cold: high 62, batch 15 used:9
cpu 3 hot: high 186, batch 31 used:13
cpu 3 cold: high 62, batch 15 used:14
cpu 4 hot: high 186, batch 31 used:0
cpu 4 cold: high 62, batch 15 used:0
cpu 5 hot: high 186, batch 31 used:0
cpu 5 cold: high 62, batch 15 used:0
cpu 6 hot: high 186, batch 31 used:0
cpu 6 cold: high 62, batch 15 used:0
cpu 7 hot: high 186, batch 31 used:0
cpu 7 cold: high 62, batch 15 used:0
cpu 8 hot: high 186, batch 31 used:81
cpu 8 cold: high 62, batch 15 used:8
cpu 9 hot: high 186, batch 31 used:1
cpu 9 cold: high 62, batch 15 used:13
cpu 10 hot: high 186, batch 31 used:69
cpu 10 cold: high 62, batch 15 used:14
cpu 11 hot: high 186, batch 31 used:77
cpu 11 cold: high 62, batch 15 used:10
cpu 12 hot: high 186, batch 31 used:0
cpu 12 cold: high 62, batch 15 used:0
cpu 13 hot: high 186, batch 31 used:135
cpu 13 cold: high 62, batch 15 used:0
cpu 14 hot: high 186, batch 31 used:0
cpu 14 cold: high 62, batch 15 used:0
cpu 15 hot: high 186, batch 31 used:0
cpu 15 cold: high 62, batch 15 used:0
Node 0 HighMem per-cpu: empty
Node 1 DMA per-cpu: empty
Node 1 DMA32 per-cpu: empty
Node 1 Normal per-cpu:
cpu 0 hot: high 186, batch 31 used:1
cpu 0 cold: high 62, batch 15 used:0
cpu 1 hot: high 186, batch 31 used:0
cpu 1 cold: high 62, batch 15 used:0
cpu 2 hot: high 186, batch 31 used:0
cpu 2 cold: high 62, batch 15 used:0
cpu 3 hot: high 186, batch 31 used:0
cpu 3 cold: high 62, batch 15 used:0
cpu 4 hot: high 186, batch 31 used:87
cpu 4 cold: high 62, batch 15 used:10
cpu 5 hot: high 186, batch 31 used:30
cpu 5 cold: high 62, batch 15 used:12
cpu 6 hot: high 186, batch 31 used:77
cpu 6 cold: high 62, batch 15 used:13
cpu 7 hot: high 186, batch 31 used:28
cpu 7 cold: high 62, batch 15 used:2
cpu 8 hot: high 186, batch 31 used:34
cpu 8 cold: high 62, batch 15 used:0
cpu 9 hot: high 186, batch 31 used:94
cpu 9 cold: high 62, batch 15 used:0
cpu 10 hot: high 186, batch 31 used:0
cpu 10 cold: high 62, batch 15 used:0
cpu 11 hot: high 186, batch 31 used:0
cpu 11 cold: high 62, batch 15 used:0
cpu 12 hot: high 186, batch 31 used:0
cpu 12 cold: high 62, batch 15 used:8
cpu 13 hot: high 186, batch 31 used:33
cpu 13 cold: high 62, batch 15 used:8
cpu 14 hot: high 186, batch 31 used:133
cpu 14 cold: high 62, batch 15 used:2
cpu 15 hot: high 186, batch 31 used:155
cpu 15 cold: high 62, batch 15 used:5
Node 1 HighMem per-cpu: empty
Free pages: 962792kB (0kB HighMem)
Active:4471040 inactive:1118163 dirty:52 writeback:0 unstable:0 free:240698 slab:283135 mapped-file:6766 mapped-anon:2481065 pagetables:10524
Node 0 DMA free:10836kB min:8kB low:8kB high:12kB active:0kB inactive:0kB present:10452kB pages_scanned:0 all_unreclaimable? yes
lowmem_reserve[]: 0 2991 12081 12081
Node 0 DMA32 free:66704kB min:2460kB low:3072kB high:3688kB active:2650608kB inactive:122492kB present:3063584kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 9090 9090
Node 0 Normal free:39604kB min:7476kB low:9344kB high:11212kB active:8293932kB inactive:618776kB present:9308160kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 0 0
Node 0 HighMem free:0kB min:128kB low:128kB high:128kB active:0kB inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 0 0
Node 1 DMA free:0kB min:0kB low:0kB high:0kB active:0kB inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 12120 12120
Node 1 DMA32 free:0kB min:0kB low:0kB high:0kB active:0kB inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 12120 12120
Node 1 Normal free:845648kB min:9968kB low:12460kB high:14952kB active:6939620kB inactive:3731384kB present:12410880kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 0 0
Node 1 HighMem free:0kB min:128kB low:128kB high:128kB active:0kB inactive:0kB present:0kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0 0 0
Node 0 DMA: 3*4kB 3*8kB 3*16kB 2*32kB 3*64kB 2*128kB 2*256kB 1*512kB 1*1024kB 0*2048kB 2*4096kB = 10836kB
Node 0 DMA32: 4260*4kB 1224*8kB 26*16kB 1*32kB 2*64kB 1*128kB 1*256kB 0*512kB 0*1024kB 1*2048kB 9*4096kB = 66704kB
Node 0 Normal: 201*4kB 884*8kB 1117*16kB 141*32kB 2*64kB 2*128kB 1*256kB 1*512kB 0*1024kB 0*2048kB 2*4096kB = 39604kB
Node 0 HighMem: empty
Node 1 DMA: empty
Node 1 DMA32: empty
Node 1 Normal: 31200*4kB 39388*8kB 14353*16kB 3307*32kB 906*64kB 2*128kB 1*256kB 1*512kB 1*1024kB 1*2048kB 2*4096kB = 845648kB
Node 1 HighMem: empty
3108846 pagecache pages
Swap cache: add 337062, delete 336108, find 261230/261555, race 0+0
Free swap = 5005124kB
Total swap = 6289320kB
Free swap: 5005124kB
6553600 pages of RAM
417159 reserved pages
2320912 pages shared
954 pages swap cached
4. 通过vm的活动情况， /proc/vmstat
$cat /proc/vmstat
nr_anon_pages 2480490
nr_mapped 6548
nr_file_pages 3110632
nr_slab 283141
nr_page_table_pages 10334
nr_dirty 1
nr_writeback 0
nr_unstable 0
nr_bounce 0
numa_hit 59784369537
numa_miss 44505232088
numa_foreign 44505232088
numa_interleave 288929
numa_local 59783481501
numa_other 44506120124
pgpgin 6085462783
pgpgout 16203578552
pswpin 2556
pswpout 334506
pgalloc_dma 1
pgalloc_dma32 12614733
pgalloc_normal 104277734751
pgalloc_high 0
pgfree 104290591256
pgactivate 50646465
pgdeactivate 4822484
pgfault 104165467862
pgmajfault 16210
pgrefill_dma 0
pgrefill_dma32 7653915
pgrefill_normal 26774426
pgrefill_high 0
pgsteal_dma 0
pgsteal_dma32 256875
pgsteal_normal 4129645
pgsteal_high 0
pgscan_kswapd_dma 0
pgscan_kswapd_dma32 343521
pgscan_kswapd_normal 4447936
pgscan_kswapd_high 0
pgscan_direct_dma 0
pgscan_direct_dma32 0
pgscan_direct_normal 0
pgscan_direct_high 0
pginodesteal 0
slabs_scanned 4000512
kswapd_steal 4386520
kswapd_inodesteal 2810883
pageoutrun 37456
allocstall 0
pgrotated 337233
有了这些信息，我们可以详细知道内存资源是如何使用的以及目前剩余情况，为下一步的优化做些决策上的依据。信息的解读可以google相关的关键词，但是充分理解这些信息点，要对内核的VM相关部分很熟悉。
PS. 以上我粗粗的列出几点，其他的同学们可以进一步补充，多谢！
祝玩得开心！