chapter18
paging-linear-translate.py参数
第一题
问题
在做地址转换之前，让我们用模拟器来研究线性页表在给定不同参数的情况下如何改变大小。在不同参数变化时，计算线性页表的大小。一些建议输入如下，通过使用-v 标志，你可以看到填充了多少个页表项。
首先，要理解线性页表大小如何随着地址空间的增长而变化：
paging-linear-translate.py -P 1k -a 1m -p 512m -v -n 0
paging-linear-translate.py -P 1k -a 2m -p 512m -v -n 0
paging-linear-translate.py -P 1k -a 4m -p 512m -v -n 0
然后，理解线性页面大小如何随页大小的增长而变化：
paging-linear-translate.py -P 1k -a 1m -p 512m -v -n 0
paging-linear-translate.py -P 2k -a 1m -p 512m -v -n 0
paging-linear-translate.py -P 4k -a 1m -p 512m -v -n 0
在运行这些命令之前，请试着想想预期的趋势。页表大小如何随地址空间的增长而改变？随着页大小的增长呢？为什么一般来说，我们不应该使用很大的页呢？
输出太长了，只给出页表的项目数。
paging-linear-translate.py -P 1k -a 1m -p 512m -v -n 0
1024项
paging-linear-translate.py -P 1k -a 2m -p 512m -v -n 0
2048项
paging-linear-translate.py -P 1k -a 4m -p 512m -v -n 0
4096项
paging-linear-translate.py -P 1k -a 1m -p 512m -v -n 0
1024项
paging-linear-translate.py -P 2k -a 1m -p 512m -v -n 0
512项
paging-linear-translate.py -P 4k -a 1m -p 512m -v -n 0
256项
页表大小随着地址空间的增大而增大，随着页大小的增大而减小。
如果使用很大的页，会产生很多内部碎片，空间被浪费了。
第二题
问题
现在让我们做一些地址转换。从一些小例子开始，使用-u 标志更改分配给地址空间的页数。例如：
paging-linear-translate.py -P 1k -a 16k -p 32k -v -u 0
paging-linear-translate.py -P 1k -a 16k -p 32k -v -u 25
paging-linear-translate.py -P 1k -a 16k -p 32k -v -u 50
paging-linear-translate.py -P 1k -a 16k -p 32k -v -u 75
paging-linear-translate.py -P 1k -a 16k -p 32k -v -u 100
如果增加每个地址空间中的页的百分比，会发生什么？
增加百分比，更多的地址转换成功。
插句题外话
附上其中一个地址转换的分析过程：
第三题
问题
现在让我们尝试一些不同的随机种子，以及一些不同的（有时相当疯狂的）地址空间参数：
paging-linear-translate.py -P 8 -a 32 -p 1024 -v -s 1
paging-linear-translate.py -P 8k -a 32k -p 1m -v -s 2
paging-linear-translate.py -P 1m -a 256m -p 512m -v -s 3
哪些参数组合是不现实的？为什么？
太长了，不截图
[whq@whq01 vm-paging]$ python paging-linear-translate.py -P 1m -a 256m -p 512m -v -s 3 -c
ARG seed 3
ARG address space size 256m
ARG phys mem size 512m
ARG page size 1m
ARG verbose True
ARG addresses -1
The format of the page table is simple:
The high-order (left-most) bit is the VALID bit.
If the bit is 1, the rest of the entry is the PFN.
If the bit is 0, the page is not valid.
Use verbose mode (-v) if you want to print the VPN # by
each entry of the page table.
Page Table (from entry 0 down to the max size)
[ 0] 0x00000000
[ 1] 0x800000bd
[ 2] 0x80000140
[ 3] 0x00000000
[ 4] 0x00000000
[ 5] 0x80000084
[ 6] 0x00000000
[ 7] 0x800000f0
[ 8] 0x800000f3
[ 9] 0x8000004d
[ 10] 0x800001bc
[ 11] 0x8000017b
[ 12] 0x80000020
[ 13] 0x8000012e
[ 14] 0x00000000
[ 15] 0x00000000
[ 16] 0x800000f2
[ 17] 0x800001c1
[ 18] 0x800001d7
[ 19] 0x00000000
[ 20] 0x800000e3
[ 21] 0x00000000
[ 22] 0x00000000
[ 23] 0x00000000
[ 24] 0x800000df
[ 25] 0x8000009a
[ 26] 0x800000c5
[ 27] 0x00000000
[ 28] 0x8000012b
[ 29] 0x8000015d
[ 30] 0x800001b6
[ 31] 0x80000157
[ 32] 0x00000000
[ 33] 0x800001ed
[ 34] 0x80000123
[ 35] 0x8000006c
[ 36] 0x80000125
[ 37] 0x00000000
[ 38] 0x00000000
[ 39] 0x800001fa
[ 40] 0x00000000
[ 41] 0x800000d2
[ 42] 0x00000000
[ 43] 0x00000000
[ 44] 0x800001be
[ 45] 0x00000000
[ 46] 0x80000017
[ 47] 0x800000a9
[ 48] 0x800001f6
[ 49] 0x800001ff
[ 50] 0x00000000
[ 51] 0x00000000
[ 52] 0x80000010
[ 53] 0x00000000
[ 54] 0x00000000
[ 55] 0x8000004f
[ 56] 0x00000000
[ 57] 0x800000a0
[ 58] 0x800001cb
[ 59] 0x00000000
[ 60] 0x00000000
[ 61] 0x80000149
[ 62] 0x8000011e
[ 63] 0x800001e1
[ 64] 0x800000dc
[ 65] 0x80000079
[ 66] 0x00000000
[ 67] 0x8000010a
[ 68] 0x80000005
[ 69] 0x00000000
[ 70] 0x8000000a
[ 71] 0x80000143
[ 72] 0x00000000
[ 73] 0x800000ee
[ 74] 0x800000b4
[ 75] 0x80000179
[ 76] 0x00000000
[ 77] 0x00000000
[ 78] 0x00000000
[ 79] 0x00000000
[ 80] 0x800000a3
[ 81] 0x00000000
[ 82] 0x00000000
[ 83] 0x00000000
[ 84] 0x80000099
[ 85] 0x00000000
[ 86] 0x8000000d
[ 87] 0x80000178
[ 88] 0x00000000
[ 89] 0x00000000
[ 90] 0x8000007a
[ 91] 0x00000000
[ 92] 0x00000000
[ 93] 0x80000034
[ 94] 0x00000000
[ 95] 0x00000000
[ 96] 0x800000e0
[ 97] 0x80000056
[ 98] 0x00000000
[ 99] 0x800001c5
[ 100] 0x00000000
[ 101] 0x00000000
[ 102] 0x00000000
[ 103] 0x80000061
[ 104] 0x800001ad
[ 105] 0x00000000
[ 106] 0x00000000
[ 107] 0x80000148
[ 108] 0x800000b0
[ 109] 0x00000000
[ 110] 0x00000000
[ 111] 0x8000008a
[ 112] 0x00000000
[ 113] 0x00000000
[ 114] 0x00000000
[ 115] 0x00000000
[ 116] 0x00000000
[ 117] 0x800001c2
[ 118] 0x800000de
[ 119] 0x800001da
[ 120] 0x00000000
[ 121] 0x800001ac
[ 122] 0x80000109
[ 123] 0x00000000
[ 124] 0x00000000
[ 125] 0x00000000
[ 126] 0x00000000
[ 127] 0x80000092
[ 128] 0x80000163
[ 129] 0x80000127
[ 130] 0x00000000
[ 131] 0x80000057
[ 132] 0x00000000
[ 133] 0x8000010c
[ 134] 0x00000000
[ 135] 0x80000139
[ 136] 0x00000000
[ 137] 0x00000000
[ 138] 0x800000f4
[ 139] 0x00000000
[ 140] 0x800001a2
[ 141] 0x00000000
[ 142] 0x800001a5
[ 143] 0x00000000
[ 144] 0x800001b9
[ 145] 0x00000000
[ 146] 0x00000000
[ 147] 0x00000000
[ 148] 0x800000d8
[ 149] 0x00000000
[ 150] 0x80000000
[ 151] 0x00000000
[ 152] 0x00000000
[ 153] 0x00000000
[ 154] 0x00000000
[ 155] 0x800001b5
[ 156] 0x00000000
[ 157] 0x800000a1
[ 158] 0x00000000
[ 159] 0x00000000
[ 160] 0x8000012c
[ 161] 0x00000000
[ 162] 0x00000000
[ 163] 0x00000000
[ 164] 0x00000000
[ 165] 0x8000016e
[ 166] 0x00000000
[ 167] 0x00000000
[ 168] 0x00000000
[ 169] 0x00000000
[ 170] 0x80000190
[ 171] 0x00000000
[ 172] 0x8000013e
[ 173] 0x00000000
[ 174] 0x00000000
[ 175] 0x00000000
[ 176] 0x800000d7
[ 177] 0x800000eb
[ 178] 0x00000000
[ 179] 0x00000000
[ 180] 0x00000000
[ 181] 0x00000000
[ 182] 0x800001df
[ 183] 0x00000000
[ 184] 0x80000194
[ 185] 0x00000000
[ 186] 0x00000000
[ 187] 0x00000000
[ 188] 0x80000153
[ 189] 0x80000195
[ 190] 0x80000177
[ 191] 0x80000002
[ 192] 0x00000000
[ 193] 0x80000016
[ 194] 0x00000000
[ 195] 0x00000000
[ 196] 0x8000005b
[ 197] 0x00000000
[ 198] 0x8000003e
[ 199] 0x80000158
[ 200] 0x800001e7
[ 201] 0x80000198
[ 202] 0x00000000
[ 203] 0x80000105
[ 204] 0x80000036
[ 205] 0x800001de
[ 206] 0x00000000
[ 207] 0x00000000
[ 208] 0x800001a7
[ 209] 0x00000000
[ 210] 0x00000000
[ 211] 0x00000000
[ 212] 0x80000181
[ 213] 0x00000000
[ 214] 0x00000000
[ 215] 0x00000000
[ 216] 0x00000000
[ 217] 0x00000000
[ 218] 0x00000000
[ 219] 0x800001f2
[ 220] 0x00000000
[ 221] 0x80000052
[ 222] 0x80000183
[ 223] 0x80000108
[ 224] 0x00000000
[ 225] 0x00000000
[ 226] 0x00000000
[ 227] 0x800001d5
[ 228] 0x800000e2
[ 229] 0x8000005f
[ 230] 0x00000000
[ 231] 0x00000000
[ 232] 0x00000000
[ 233] 0x800001e8
[ 234] 0x00000000
[ 235] 0x800000d3
[ 236] 0x00000000
[ 237] 0x00000000
[ 238] 0x00000000
[ 239] 0x00000000
[ 240] 0x00000000
[ 241] 0x00000000
[ 242] 0x00000000
[ 243] 0x00000000
[ 244] 0x80000049
[ 245] 0x800000f5
[ 246] 0x800000ef
[ 247] 0x800001a4
[ 248] 0x800000f6
[ 249] 0x00000000
[ 250] 0x800001eb
[ 251] 0x00000000
[ 252] 0x00000000
[ 253] 0x00000000
[ 254] 0x80000159
[ 255] 0x00000000
Virtual Address Trace
VA 0x0308b24d (decimal: 50901581) --> 1f68b24d (decimal 526955085) [VPN 48]
VA 0x042351e6 (decimal: 69423590) --> Invalid (VPN 66 not valid)
VA 0x02feb67b (decimal: 50247291) --> 0a9eb67b (decimal 178173563) [VPN 47]
VA 0x0b46977d (decimal: 189175677) --> Invalid (VPN 180 not valid)
VA 0x0dbcceb4 (decimal: 230477492) --> 1f2cceb4 (decimal 523030196) [VPN 219]
这三个都存在正确的转换，因此都不能算“错误”。但是三个的组合都不太合理。
1和2：地址空间太小，只能容下4个页。
3：页大小有点大了
第四题
问题
利用该程序尝试其他一些问题。你能找到让程序无法工作的限制吗？例如，如果地址空间大小大于物理内存，会发生什么情况？
会报错，提示物理内存大小应该大于地址空间大小
