Describing Physical Memory (kernel.org)
Memory zones and a Linux driver issue (redhat.com)
virtual.dvi (uc.edu)
Zones 介绍
图片.png
32位 x86架构
| x86 zones | Size | Page |
|---|---|---|
| ZONE_DMA | First 16MiB of memory | |
| ZONE_NORMAL | 16MiB - 896MiB | |
| ZONE_HIGHMEM | 896 MiB - End |
64位 x86_64架构
| x86_64 zones | Size | Page |
|---|---|---|
| ZONE_DMA | first 16MB/24bit for I/O 内存开始的16M |
|
| ZONE_DMA32 | 4GB I/O 16MB~4GB |
|
| ZONE_NORMAL | all further memory 4GB到结束 |
这样划分内存有助于内存管理。
DMA zone 用于传输，比如网卡，24位地址，16MB。一些设备/驱动只能使用DMA zone的内存。
DMA32 zone 用于与卡交换数据，32位地址，4GB。
Normal zone 用于进程。
启动时，dmesg可以展示这3个zone的物理地址分配。
Zones优先选择 Normal > DMA32 > DMA。如果Normal有free memory，kernel则从Normal zone取内存，如果没有则从DMA32取内存。
dmesg查看Zones
范例1G内存
[sysadmin@VM_200_2_centos ~]$ free total used free shared buff/cache available Mem: 1016288 197452 97624 924 721212 642568 Swap: 0 0 0
dmesg -kT查看
[Mon Jun 8 20:57:35 2020] Zone ranges:
[Mon Jun 8 20:57:35 2020] DMA [mem 0x00001000-0x00ffffff]
[Mon Jun 8 20:57:35 2020] DMA32 [mem 0x01000000-0xffffffff]
[Mon Jun 8 20:57:35 2020] Normal empty
[Mon Jun 8 20:57:35 2020] Movable zone start for each node
[Mon Jun 8 20:57:35 2020] Early memory node ranges
[Mon Jun 8 20:57:35 2020] node 0: [mem 0x00001000-0x0009efff]
[Mon Jun 8 20:57:35 2020] node 0: [mem 0x00100000-0x3fffdfff]
[Mon Jun 8 20:57:35 2020] Initmem setup node 0 [mem 0x00001000-0x3fffdfff]
[Mon Jun 8 20:57:35 2020] On node 0 totalpages: 262044
[Mon Jun 8 20:57:35 2020] DMA zone: 64 pages used for memmap
[Mon Jun 8 20:57:35 2020] DMA zone: 21 pages reserved
[Mon Jun 8 20:57:35 2020] DMA zone: 3998 pages, LIFO batch:0
[Mon Jun 8 20:57:35 2020] DMA32 zone: 4032 pages used for memmap
[Mon Jun 8 20:57:35 2020] DMA32 zone: 258046 pages, LIFO batch:31
DMA [mem 0x00001000-0x00ffffff]
0x00000000 - 0x00001000 之间存在1页(4096字节)。去哪了？
加上该页才能凑齐4096页=16MB
1G内存 = 262,144页 = 0x3fffffff
0x3fffdfff = 262,142页
0x3fffdfff - 0x3fffffff 之间的2页去哪了？
0xffffffff = 4g
(0x3fffdfff - 0x00001000) = (1073733631 - 4096) = 1,073,729,535
(1073729535+1)/4096 = 262141 页 ， 与totalpages: 262044相比多100页，这100页去哪了？
1143 [Fri May 7 18:52:02 2021] Mem-Info:
1144 [Fri May 7 18:52:02 2021] active_anon:207723 inactive_anon:72 isolated_anon:0
1145 active_file:2645 inactive_file:6379 isolated_file:0
1146 unevictable:0 dirty:0 writeback:0 unstable:0
1147 slab_reclaimable:6455 slab_unreclaimable:3695
1148 mapped:1656 shmem:210 pagetables:3268 bounce:0
1149 free:12216 free_pcp:30 free_cma:0
1150 [Fri May 7 18:52:02 2021] Node 0 DMA free:4600kB min:704kB low:880kB high:1056kB active_anon:9560kB inactive_anon:4kB active_file:16kB inactive_file:520kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15908kB mlock ed:0kB dirty:0kB writeback:0kB mapped:32kB shmem:4kB slab_reclaimable:384kB slab_unreclaimable:144kB kernel_stack:80kB pagetables:160kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:1152 all_unrecl aimable? yes
1151 [Fri May 7 18:52:02 2021] lowmem_reserve[]: 0 975 975 975
1152 [Fri May 7 18:52:02 2021] Node 0 DMA32 free:44264kB min:44348kB low:55432kB high:66520kB active_anon:821332kB inactive_anon:284kB active_file:10564kB inactive_file:24996kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:1032184kB ma naged:1000380kB mlocked:0kB dirty:0kB writeback:0kB mapped:6592kB shmem:836kB slab_reclaimable:25436kB slab_unreclaimable:14636kB kernel_stack:2880kB pagetables:12912kB unstable:0kB bounce:0kB free_pcp:120kB local_pcp:120kB free_cma:0kB writeback_ tmp:0kB pages_scanned:0 all_unreclaimable? no
1153 [Fri May 7 18:52:02 2021] lowmem_reserve[]: 0 0 0 0
1154 [Fri May 7 18:52:02 2021] Node 0 DMA: 12*4kB (UE) 21*8kB (UE) 14*16kB (UEM) 10*32kB (UE) 6*64kB (UEM) 3*128kB (U) 2*256kB (UE) 1*512kB (M) 2*1024kB (EM) 0*2048kB 0*4096kB = 4600kB
1155 [Fri May 7 18:52:02 2021] Node 0 DMA32: 332*4kB (UEM) 465*8kB (UE) 503*16kB (UEM) 303*32kB (UEM) 194*64kB (UEM) 37*128kB (UE) 11*256kB (UEM) 3*512kB (M) 0*1024kB 0*2048kB 0*4096kB = 44296kB
1156 [Fri May 7 18:52:02 2021] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
1157 [Fri May 7 18:52:02 2021] 9248 total pagecache pages
1158 [Fri May 7 18:52:02 2021] 0 pages in swap cache
1159 [Fri May 7 18:52:02 2021] Swap cache stats: add 0, delete 0, find 0/0
1160 [Fri May 7 18:52:02 2021] Free swap = 0kB
1161 [Fri May 7 18:52:02 2021] Total swap = 0kB
1162 [Fri May 7 18:52:02 2021] 262044 pages RAM
1163 [Fri May 7 18:52:02 2021] 0 pages HighMem/MovableOnly
1164 [Fri May 7 18:52:02 2021] 7972 pages reserved
-
/proc/buddyinfo查看明细
[sysadmin@VM_200_2_centos ~]$ cat /proc/buddyinfo
Node 0, zone DMA 7 13 20 9 9 3 4 2 1 0 0
Node 0, zone DMA32 1387 2527 946 434 239 49 23 0 0 0 0
最左侧列显示，DMA有 7 个4k free page，DMA32有 1387 个4k free page。
没有NORMAL（1G内存嘛~）。
图片.png
Buddy memory allocation - Wikipedia
/proc/buddyinfo (archive.org)
-
/proc/pagetypeinfo查看更详细信息
2G内存
[root@localhost ~]# cat /proc/pagetypeinfo
Page block order: 9
Pages per block: 512
Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone DMA, type Unmovable 1 3 2 3 1 0 1 1 0 0 0
Node 0, zone DMA, type Reclaimable 0 5 5 2 2 0 0 1 1 1 0
Node 0, zone DMA, type Movable 7 2 2 0 1 0 1 0 1 1 0
Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Unmovable 0 18 114 102 75 35 8 0 0 0 0
Node 0, zone DMA32, type Reclaimable 1 1 0 34 168 0 0 0 0 0 0
Node 0, zone DMA32, type Movable 1 0 21 217 39 12 4 1 3 4 1
Node 0, zone DMA32, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Number of blocks type Unmovable Reclaimable Movable Reserve CMA Isolate
Node 0, zone DMA 1 2 5 0 0 0
Node 0, zone DMA32 57 23 936 0 0 0
4G内存
[sysadmin@prod-proxy ~]$ cat /proc/pagetypeinfo
Page block order: 9
Pages per block: 512
Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone DMA, type Unmovable 2 0 0 1 1 0 1 0 1 0 0
Node 0, zone DMA, type Reclaimable 2 2 1 0 1 1 1 1 1 1 0
Node 0, zone DMA, type Movable 0 3 0 1 1 1 0 1 1 0 2
Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Unmovable 0 235 389 197 75 25 3 1 1 0 0
Node 0, zone DMA32, type Reclaimable 32 320 325 227 88 32 11 0 1 1 0
Node 0, zone DMA32, type Movable 0 1489 2651 1228 656 162 11 9 1 4 2
Node 0, zone DMA32, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Unmovable 57 129 126 73 36 10 1 1 0 0 0
Node 0, zone Normal, type Reclaimable 45 123 87 53 13 7 3 0 0 0 0
Node 0, zone Normal, type Movable 0 551 1176 524 127 28 3 5 1 1 0
Node 0, zone Normal, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type CMA 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
Number of blocks type Unmovable Reclaimable Movable Reserve CMA Isolate
Node 0, zone DMA 1 2 5 0 0 0
Node 0, zone DMA32 973 22 533 0 0 0
Node 0, zone Normal 329 8 175 0 0 0
16G内存
[sysadmin@VM_1_13_centos ~]$ cat /proc/pagetypeinfo
Page block order: 9
Pages per block: 512
Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone DMA, type Unmovable 1 0 0 0 2 1 1 0 1 0 0
Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type Movable 0 0 0 0 0 0 0 0 0 1 3
Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Unmovable 22 5 1 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Reclaimable 18301 16290 18959 18 0 0 0 0 0 0 0
Node 0, zone DMA32, type Movable 2 3 4 7 0 0 0 0 0 0 0
Node 0, zone DMA32, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Unmovable 9190 6730 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Reclaimable 126786 124911 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Movable 1 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Reserve 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type CMA 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
Number of blocks type Unmovable Reclaimable Movable Reserve CMA Isolate
Node 0, zone DMA 1 0 7 0 0 0
Node 0, zone DMA32 4 1652 128 0 0 0
Node 0, zone Normal 359 5625 416 0 0 0
根据buddyinfo计算free内存 (不确定哦~)
[sysadmin@VM_200_2_centos ~]$ free
total used free shared buff/cache available
Mem: 1016288 149756 84916 828 781616 685284
Swap: 0 0 0
[sysadmin@VM_200_2_centos ~]$ cat /proc/buddyinfo
Node 0, zone DMA 37 16 33 7 7 5 3 2 1 0 0
Node 0, zone DMA32 1021 2132 830 454 269 77 15 0 0 0 0
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