1.1 --- a/docs/wiki/ProgramLoading Wed Aug 10 23:58:38 2022 +0200
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,236 +0,0 @@
1.4 -= Program Loading =
1.5 -
1.6 -The provision of [[Paging|paging]] of file content leads to the possibility of
1.7 -demand paging for programs, enabling them to be loaded into memory dynamically
1.8 -and to have only the active portions of those programs resident. To achieve
1.9 -this, programs must be appropriately initialised in new tasks, with a page
1.10 -fault handler configured to provide program file content whenever a region of
1.11 -the program payload is encountered that is not currently resident in memory.
1.12 -
1.13 -== Internal Page Fault Handlers ==
1.14 -
1.15 -When satisfying page faults for a task, one approach involves situating the
1.16 -page fault handler within the task itself, this managing the available memory
1.17 -regions and employing receive windows when requesting memory pages.
1.18 -
1.19 -The general arrangement involving such internal page fault handlers for a
1.20 -program in a task is as follows:
1.21 -
1.22 -######## A graph showing the internal paging mechanism
1.23 -
1.24 -{{{#!graphviz
1.25 -#format svg
1.26 -#transform notugly
1.27 -digraph internal_paging {
1.28 - node [fontsize="12.0",fontname="sans-serif",shape=box];
1.29 - edge [fontsize="12.0",fontname="sans-serif"];
1.30 - rankdir=LR;
1.31 -
1.32 - TaskMemory [shape=record,label="Task Memory |<s> stack | ... |<d> data | ... |<c> code"];
1.33 -
1.34 - subgraph {
1.35 - rank=same;
1.36 -
1.37 - InternalPager;
1.38 - InternalPager_note [shape=note,style=filled,fillcolor=gold,label="Resides in\nsame task and\ndefines scope of\nfault resolution"];
1.39 -
1.40 - InternalPager -> InternalPager_note [dir=none,style=dotted];
1.41 - }
1.42 -
1.43 - subgraph {
1.44 - rank=same;
1.45 -
1.46 - Regions [shape=record,label="Regions |
1.47 - {<s> stack |<sd> stack-dataspace } |
1.48 - {<d> data | <dd> data-dataspace } |
1.49 - {<c> code |<cd> code-dataspace } |..."];
1.50 -
1.51 - ReceiveFlexpage [shape=note,label="Flexpage\n(receive window)"];
1.52 -
1.53 - Flexpage [shape=note];
1.54 - Flexpage_note [shape=note,style=filled,fillcolor=gold,label="Satisfies\nmemory\naccess"];
1.55 -
1.56 - Flexpage -> Flexpage_note [dir=none,style=dotted];
1.57 - }
1.58 -
1.59 - subgraph {
1.60 - rank=same;
1.61 -
1.62 - ResourceD [label="Resource\n(Pager)"];
1.63 - ResourceD_note [shape=note,style=filled,fillcolor=gold,label="Provides access\nto file content"];
1.64 -
1.65 - ResourceD -> ResourceD_note [dir=none,style=dotted];
1.66 - }
1.67 -
1.68 - ProgramFile [shape=record,label="Program File | ... |<d> data |<c> code | ..."];
1.69 -
1.70 - /* Page fault handling. */
1.71 -
1.72 - TaskMemory:d -> InternalPager [label="page fault"];
1.73 -
1.74 - InternalPager -> Regions:d [label="find region"];
1.75 -
1.76 - Regions:dd -> ResourceD [style=dashed];
1.77 -
1.78 - InternalPager -> ReceiveFlexpage [dir=none];
1.79 - ReceiveFlexpage -> ResourceD [label="map"];
1.80 -
1.81 - ResourceD -> ProgramFile:d [style=dashed];
1.82 -
1.83 - ResourceD -> Flexpage [dir=none];
1.84 - Flexpage -> InternalPager;
1.85 -}
1.86 -}}}
1.87 -
1.88 -########
1.89 -
1.90 -== External Page Fault Handlers ==
1.91 -
1.92 -Another approach that may be used to support an internal page fault handler
1.93 -deployed in a task is to employ an external page fault handler in the creating
1.94 -task. When a page fault occurs, the external handler ensures that the
1.95 -appropriate content has been brought into its own memory space. It then
1.96 -returns a flexpage from the handler routine to resolve the fault.
1.97 -
1.98 -######## A graph showing the external paging mechanism
1.99 -
1.100 -{{{#!graphviz
1.101 -#format svg
1.102 -#transform notugly
1.103 -digraph external_paging {
1.104 - node [fontsize="12.0",fontname="sans-serif",shape=box];
1.105 - edge [fontsize="12.0",fontname="sans-serif"];
1.106 - rankdir=LR;
1.107 -
1.108 - TaskMemory [shape=record,label="Task Memory |<s> stack | ... |<d> data | ... |<c> code"];
1.109 -
1.110 - subgraph {
1.111 - rank=same;
1.112 -
1.113 - ExternalPager_note [shape=note,style=filled,fillcolor=gold,label="Resides in\nseparate task"];
1.114 - ExternalPager;
1.115 -
1.116 - ExternalPager_note -> ExternalPager [dir=none,style=dotted];
1.117 -
1.118 - MappedFlexpage [shape=note,label="Flexpage\n(positioned)"];
1.119 - MappedFlexpage_note [shape=note,style=filled,fillcolor=gold,label="Satisfies\nmemory\naccess"];
1.120 -
1.121 - MappedFlexpage -> MappedFlexpage_note [dir=none,style=dotted];
1.122 - }
1.123 -
1.124 - subgraph {
1.125 - rank=same;
1.126 -
1.127 - Regions [shape=record,label="Regions |
1.128 - {<s> stack |<sd> stack-dataspace } |
1.129 - {<d> data | <dd> data-dataspace } |
1.130 - {<c> code |<cd> code-dataspace } |..."];
1.131 -
1.132 - L4Re [shape=ellipse,label="L4Re paging\nfunctionality"];
1.133 - L4Re_note [shape=note,style=filled,fillcolor=gold,label="Supports normal\naccess to file content"];
1.134 -
1.135 - L4Re -> L4Re_note [dir=none,style=dotted];
1.136 -
1.137 - Flexpage [shape=note];
1.138 - }
1.139 -
1.140 - subgraph {
1.141 - rank=same;
1.142 -
1.143 - ResourceD [label="Resource\n(Pager)"];
1.144 - ResourceD_note [shape=note,style=filled,fillcolor=gold,label="Provides access\nto file content"];
1.145 -
1.146 - ResourceD -> ResourceD_note [dir=none,style=dotted];
1.147 - }
1.148 -
1.149 - ProgramFile [shape=record,label="Program File | ... |<d> data |<c> code | ..."];
1.150 -
1.151 - /* Page fault handling. */
1.152 -
1.153 - TaskMemory:d -> ExternalPager [label="page fault"];
1.154 -
1.155 - ExternalPager -> Regions:d [label="find region"];
1.156 -
1.157 - Regions:dd -> ResourceD [style=dashed];
1.158 -
1.159 - ExternalPager -> L4Re;
1.160 - L4Re -> ResourceD [label="map"];
1.161 -
1.162 - ResourceD -> ProgramFile:d [style=dashed];
1.163 -
1.164 - ResourceD -> Flexpage [dir=none];
1.165 - Flexpage -> ExternalPager;
1.166 -
1.167 - ExternalPager -> MappedFlexpage [dir=none];
1.168 - MappedFlexpage -> TaskMemory:d;
1.169 -}
1.170 -}}}
1.171 -
1.172 -########
1.173 -
1.174 -== Configuring Programs ==
1.175 -
1.176 -To provide an internal page fault handler alongside an actual program to be
1.177 -run, the following arrangement is used:
1.178 -
1.179 -######## A graph showing the configuration arrangement
1.180 -
1.181 -{{{#!graphviz
1.182 -#format svg
1.183 -#transform notugly
1.184 -digraph program_configuration {
1.185 - node [fontsize="12.0",fontname="sans-serif",shape=box];
1.186 - edge [fontsize="12.0",fontname="sans-serif"];
1.187 - rankdir=LR;
1.188 -
1.189 - subgraph {
1.190 - rank=min;
1.191 -
1.192 - CreatingTask_note [shape=note,style=filled,fillcolor=gold,label="Responsible for\ncreating the\nnew task"];
1.193 - CreatingTask [label="Creating task"];
1.194 -
1.195 - CreatingTask_note -> CreatingTask [dir=none,style=dotted];
1.196 - }
1.197 -
1.198 - subgraph {
1.199 - rank=max;
1.200 -
1.201 - IPCGate_note [shape=note,style=filled,fillcolor=gold,label="Created for sharing\nbetween the tasks"];
1.202 - IPCGate [shape=octagon,label="IPC gate"];
1.203 -
1.204 - IPCGate_note -> IPCGate [dir=none,style=dotted];
1.205 - }
1.206 -
1.207 - InitCaps [shape=record,label="<head> Initial capabilities | {<s> \"server\" |<c> capability }"];
1.208 -
1.209 - subgraph {
1.210 - rank=same;
1.211 -
1.212 - InternalPager;
1.213 - InternalPager_note [shape=note,style=filled,fillcolor=gold,label="Starts and binds\nto IPC gate"];
1.214 -
1.215 - InternalPager -> InternalPager_note [dir=none,style=dotted];
1.216 -
1.217 - Program;
1.218 - Program_note [shape=note,style=filled,fillcolor=gold,label="Starts and references\npager via IPC gate"];
1.219 -
1.220 - Program -> Program_note [dir=none,style=dotted];
1.221 - }
1.222 -
1.223 - /* Create and transfer IPC gate for binding. */
1.224 -
1.225 - CreatingTask -> IPCGate [label="create"];
1.226 - CreatingTask -> InitCaps:head [label="define"];
1.227 - InitCaps:c -> IPCGate;
1.228 -
1.229 - /* Thread initiation. */
1.230 -
1.231 - CreatingTask -> InternalPager [label="start"];
1.232 - InternalPager -> InitCaps:s [label="bind"];
1.233 -
1.234 - CreatingTask -> Program [label="start"];
1.235 - Program -> IPCGate -> InternalPager [style=dashed];
1.236 -}
1.237 -}}}
1.238 -
1.239 -########