1# Virtual Memory Management<a name="EN-US_TOPIC_0000001123800847"></a> 2 3- [Basic Concepts](#section650193717411) 4- [Working Principles](#section072885512412) 5- [Development Guidelines](#section20956116050) 6 - [Available APIs](#section166137221657) 7 - [How to Develop](#section8752103914513) 8 9 10## Basic Concepts<a name="section650193717411"></a> 11 12Virtual memory management is a technology used by computer systems to manage memory. Each process has a continuous virtual address space. The size of the virtual address space is determined by the number of CPU bits. The maximum addressing space for a 32-bit hardware platform ranges from 0 GiB to 4 GiB. The 4 GiB space is divided into two parts: 3 GiB higher-address space for the LiteOS-A kernel and 1 GiB lower-address space for processes. The virtual address space of each process space is independent, and the code and data do not affect each other. 13 14The system divides the virtual memory into memory blocks called virtual pages. The size of a virtual page is generally 4 KiB or 64 KiB. The virtual page of the LiteOS-A kernel is 4 KiB by default. You can configure memory management units \(MMUs\) as required. The minimum unit of the virtual memory management is a page. A virtual address region in the LiteOS-A kernel can contain one virtual page or multiple virtual pages with contiguous addresses. Similarly, the physical memory is also divided by page, and each memory block is called page frame. The virtual address space is divided as follows: 3 GiB \(**0x40000000** to **0xFFFFFFFF**\) for the kernel space and 1 GiB \(**0x01000000** to **0x3F000000**\) for the user space. The following tables describe the virtual address plan. You can view or configure virtual addresses in **los\_vm\_zone.h**. 15 16**Table 1** Kernel-space addresses 17 18<a name="table9988174163613"></a> 19<table><thead align="left"><tr id="row164675173616"><th class="cellrowborder" valign="top" width="19.99%" id="mcps1.2.4.1.1"><p id="p046752361"><a name="p046752361"></a><a name="p046752361"></a>Zone</p> 20</th> 21<th class="cellrowborder" valign="top" width="43.13%" id="mcps1.2.4.1.2"><p id="p0461651361"><a name="p0461651361"></a><a name="p0461651361"></a>Description</p> 22</th> 23<th class="cellrowborder" valign="top" width="36.88%" id="mcps1.2.4.1.3"><p id="p446195183611"><a name="p446195183611"></a><a name="p446195183611"></a>Property</p> 24</th> 25</tr> 26</thead> 27<tbody><tr id="row94619516367"><td class="cellrowborder" valign="top" width="19.99%" headers="mcps1.2.4.1.1 "><p id="p1846553363"><a name="p1846553363"></a><a name="p1846553363"></a>DMA zone</p> 28</td> 29<td class="cellrowborder" valign="top" width="43.13%" headers="mcps1.2.4.1.2 "><p id="p3461158364"><a name="p3461158364"></a><a name="p3461158364"></a>Addresses for direct memory access (DMA) of I/O devices.</p> 30</td> 31<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p10461152363"><a name="p10461152363"></a><a name="p10461152363"></a>Uncache</p> 32</td> 33</tr> 34<tr id="row246551361"><td class="cellrowborder" valign="top" width="19.99%" headers="mcps1.2.4.1.1 "><p id="p3461259362"><a name="p3461259362"></a><a name="p3461259362"></a>Normal zone</p> 35</td> 36<td class="cellrowborder" valign="top" width="43.13%" headers="mcps1.2.4.1.2 "><p id="p1546056362"><a name="p1546056362"></a><a name="p1546056362"></a>Addresses for loading the kernel code segment, data segment, heap, and stack.</p> 37</td> 38<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p646125143613"><a name="p646125143613"></a><a name="p646125143613"></a>Cache</p> 39</td> 40</tr> 41<tr id="row646165133613"><td class="cellrowborder" valign="top" width="19.99%" headers="mcps1.2.4.1.1 "><p id="p114675183615"><a name="p114675183615"></a><a name="p114675183615"></a>high mem zone</p> 42</td> 43<td class="cellrowborder" valign="top" width="43.13%" headers="mcps1.2.4.1.2 "><p id="p194611583613"><a name="p194611583613"></a><a name="p194611583613"></a>Addresses for allocating contiguous virtual memory. The mapped physical memory blocks may not be contiguous.</p> 44</td> 45<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p8461153369"><a name="p8461153369"></a><a name="p8461153369"></a>Cache</p> 46</td> 47</tr> 48</tbody> 49</table> 50 51**Table 2** User-space virtual addresses 52 53<a name="table19965411366"></a> 54<table><thead align="left"><tr id="row646185183618"><th class="cellrowborder" valign="top" width="20%" id="mcps1.2.4.1.1"><p id="p3466593612"><a name="p3466593612"></a><a name="p3466593612"></a>Zone</p> 55</th> 56<th class="cellrowborder" valign="top" width="43.120000000000005%" id="mcps1.2.4.1.2"><p id="p84645143613"><a name="p84645143613"></a><a name="p84645143613"></a>Description</p> 57</th> 58<th class="cellrowborder" valign="top" width="36.88%" id="mcps1.2.4.1.3"><p id="p1146115203615"><a name="p1146115203615"></a><a name="p1146115203615"></a>Property</p> 59</th> 60</tr> 61</thead> 62<tbody><tr id="row7462511363"><td class="cellrowborder" valign="top" width="20%" headers="mcps1.2.4.1.1 "><p id="p2467516363"><a name="p2467516363"></a><a name="p2467516363"></a>Code segment</p> 63</td> 64<td class="cellrowborder" valign="top" width="43.120000000000005%" headers="mcps1.2.4.1.2 "><p id="p7472523618"><a name="p7472523618"></a><a name="p7472523618"></a>User-space code segment address range</p> 65</td> 66<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p14476563611"><a name="p14476563611"></a><a name="p14476563611"></a>Cache</p> 67</td> 68</tr> 69<tr id="row34755153614"><td class="cellrowborder" valign="top" width="20%" headers="mcps1.2.4.1.1 "><p id="p194735173612"><a name="p194735173612"></a><a name="p194735173612"></a>Heap</p> 70</td> 71<td class="cellrowborder" valign="top" width="43.120000000000005%" headers="mcps1.2.4.1.2 "><p id="p114720518362"><a name="p114720518362"></a><a name="p114720518362"></a>User-space heap address range</p> 72</td> 73<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p9474515364"><a name="p9474515364"></a><a name="p9474515364"></a>Cache</p> 74</td> 75</tr> 76<tr id="row9476518368"><td class="cellrowborder" valign="top" width="20%" headers="mcps1.2.4.1.1 "><p id="p34714516369"><a name="p34714516369"></a><a name="p34714516369"></a>Stack</p> 77</td> 78<td class="cellrowborder" valign="top" width="43.120000000000005%" headers="mcps1.2.4.1.2 "><p id="p74705163612"><a name="p74705163612"></a><a name="p74705163612"></a>User-space stack address range</p> 79</td> 80<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p144775143613"><a name="p144775143613"></a><a name="p144775143613"></a>Cache</p> 81</td> 82</tr> 83<tr id="row1047353364"><td class="cellrowborder" valign="top" width="20%" headers="mcps1.2.4.1.1 "><p id="p1947145163615"><a name="p1947145163615"></a><a name="p1947145163615"></a>Shared library</p> 84</td> 85<td class="cellrowborder" valign="top" width="43.120000000000005%" headers="mcps1.2.4.1.2 "><p id="p24745193617"><a name="p24745193617"></a><a name="p24745193617"></a>Address range for loading the user-space shared library, including the address range mapped by mmap.</p> 86</td> 87<td class="cellrowborder" valign="top" width="36.88%" headers="mcps1.2.4.1.3 "><p id="p11472510363"><a name="p11472510363"></a><a name="p11472510363"></a>Cache</p> 88</td> 89</tr> 90</tbody> 91</table> 92 93## Working Principles<a name="section072885512412"></a> 94 95In virtual memory management, the virtual address space is contiguous, but the mapped physical memory is not necessarily contiguous, as shown in the following figure. When an executable program is loaded and runs, the CPU accesses the code or data in the virtual address space in the following two cases: 96 97- If the page \(for example, V0\) containing the virtual address accessed by the CPU is mapped to a physical page \(for example, P0\), the CPU locates the page table entry corresponding to the process \(for details, see [Virtual-to-Physical Mapping](kernel-small-basic-inner-reflect.md)"\), accesses the physical memory based on the physical address information in the page table entry, and returns the content. 98- If the page \(for example, V2\) containing the virtual address accessed by the CPU is not mapped to a physical page, the system triggers a page missing fault, requests a physical page, copies the corresponding information to the physical page, and updates the start address of the physical page to the page table entry. Then, the CPU can access specific code or data by executing the instruction for accessing the virtual memory again. 99 100**Figure 1** Mapping between the virtual and physical memory addresses<a name="fig144371159135620"></a> 101 102 103## Development Guidelines<a name="section20956116050"></a> 104 105### Available APIs<a name="section166137221657"></a> 106 107**Table 3** Virtual memory management module APIs 108 109<a name="table1415203765610"></a> 110<table><thead align="left"><tr id="row134151837125611"><th class="cellrowborder" valign="top" width="12.811281128112812%" id="mcps1.2.4.1.1"><p id="p16415637105612"><a name="p16415637105612"></a><a name="p16415637105612"></a>Category</p> 111</th> 112<th class="cellrowborder" valign="top" width="29.84298429842984%" id="mcps1.2.4.1.2"><p id="p11415163718562"><a name="p11415163718562"></a><a name="p11415163718562"></a>API</p> 113</th> 114<th class="cellrowborder" valign="top" width="57.34573457345735%" id="mcps1.2.4.1.3"><p id="p1641533755612"><a name="p1641533755612"></a><a name="p1641533755612"></a>Description</p> 115</th> 116</tr> 117</thead> 118<tbody><tr id="row0415737175610"><td class="cellrowborder" rowspan="5" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p4917132105710"><a name="p4917132105710"></a><a name="p4917132105710"></a>Obtaining process memory space</p> 119</td> 120<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p341513372561"><a name="p341513372561"></a><a name="p341513372561"></a>LOS_CurrSpaceGet</p> 121</td> 122<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p74151037185617"><a name="p74151037185617"></a><a name="p74151037185617"></a>Obtains the pointer to the current process space structure.</p> 123</td> 124</tr> 125<tr id="row1841519376561"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p64151837155618"><a name="p64151837155618"></a><a name="p64151837155618"></a>LOS_SpaceGet</p> 126</td> 127<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p441516379562"><a name="p441516379562"></a><a name="p441516379562"></a>Obtains the pointer to the process space structure corresponding to the virtual address.</p> 128</td> 129</tr> 130<tr id="row536885134010"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p236819594010"><a name="p236819594010"></a><a name="p236819594010"></a>LOS_GetKVmSpace</p> 131</td> 132<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p736918564019"><a name="p736918564019"></a><a name="p736918564019"></a>Obtains the pointer to the kernel process space structure.</p> 133</td> 134</tr> 135<tr id="row11567448194112"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p0568204814115"><a name="p0568204814115"></a><a name="p0568204814115"></a>LOS_GetVmallocSpace</p> 136</td> 137<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p05681348204114"><a name="p05681348204114"></a><a name="p05681348204114"></a>Obtains the pointer to the vmalloc space structure.</p> 138</td> 139</tr> 140<tr id="row1141513373562"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p17765212416"><a name="p17765212416"></a><a name="p17765212416"></a>LOS_GetVmSpaceList</p> 141</td> 142<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1972971913115"><a name="p1972971913115"></a><a name="p1972971913115"></a>Obtains the pointer to the process space linked list.</p> 143</td> 144</tr> 145<tr id="row137812054195014"><td class="cellrowborder" rowspan="15" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p15344719152113"><a name="p15344719152113"></a><a name="p15344719152113"></a>Operations related to the virtual address region</p> 146</td> 147<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p97821654195014"><a name="p97821654195014"></a><a name="p97821654195014"></a>LOS_RegionFind</p> 148</td> 149<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p137821854205011"><a name="p137821854205011"></a><a name="p137821854205011"></a>Checks whether a virtual address region exists in the process space based on the start address.</p> 150</td> 151</tr> 152<tr id="row254713575505"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p954785720501"><a name="p954785720501"></a><a name="p954785720501"></a>LOS_RegionRangeFind</p> 153</td> 154<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p20547557175013"><a name="p20547557175013"></a><a name="p20547557175013"></a>Checks whether a virtual address region exists in the process space based on the address region.</p> 155</td> 156</tr> 157<tr id="row1692045119"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1510110115114"><a name="p1510110115114"></a><a name="p1510110115114"></a>LOS_IsRegionFileValid</p> 158</td> 159<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p61011045112"><a name="p61011045112"></a><a name="p61011045112"></a>Checks whether the virtual address region is mapped to a file.</p> 160</td> 161</tr> 162<tr id="row186701424548"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1967018210546"><a name="p1967018210546"></a><a name="p1967018210546"></a>LOS_RegionAlloc</p> 163</td> 164<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p196701221548"><a name="p196701221548"></a><a name="p196701221548"></a>Requests a free virtual address region.</p> 165</td> 166</tr> 167<tr id="row1955586175412"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p555626195420"><a name="p555626195420"></a><a name="p555626195420"></a>LOS_RegionFree</p> 168</td> 169<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p85568612547"><a name="p85568612547"></a><a name="p85568612547"></a>Releases a specific region in the process space.</p> 170</td> 171</tr> 172<tr id="row259111510282"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p3591135110288"><a name="p3591135110288"></a><a name="p3591135110288"></a>LOS_RegionEndAddr</p> 173</td> 174<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p4675183817474"><a name="p4675183817474"></a><a name="p4675183817474"></a>Obtains the end address of the specified address region.</p> 175</td> 176</tr> 177<tr id="row12894115716285"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p889418577280"><a name="p889418577280"></a><a name="p889418577280"></a>LOS_RegionSize</p> 178</td> 179<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p68941757112813"><a name="p68941757112813"></a><a name="p68941757112813"></a>Obtains the size of a region.</p> 180</td> 181</tr> 182<tr id="row14931456182812"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1293135611287"><a name="p1293135611287"></a><a name="p1293135611287"></a>LOS_IsRegionTypeFile</p> 183</td> 184<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1393185613288"><a name="p1393185613288"></a><a name="p1393185613288"></a>Checks whether it is a file memory mapping.</p> 185</td> 186</tr> 187<tr id="row12153854132814"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p115335452819"><a name="p115335452819"></a><a name="p115335452819"></a>LOS_IsRegionPermUserReadOnly</p> 188</td> 189<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1415314545285"><a name="p1415314545285"></a><a name="p1415314545285"></a>Checks whether the address region is read-only in the user space.</p> 190</td> 191</tr> 192<tr id="row29249497282"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1492415495284"><a name="p1492415495284"></a><a name="p1492415495284"></a>LOS_IsRegionFlagPrivateOnly</p> 193</td> 194<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1392434982817"><a name="p1392434982817"></a><a name="p1392434982817"></a>Checks whether the address region has private attributes.</p> 195</td> 196</tr> 197<tr id="row1233194042814"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p3339401289"><a name="p3339401289"></a><a name="p3339401289"></a>LOS_SetRegionTypeFile</p> 198</td> 199<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p193317409285"><a name="p193317409285"></a><a name="p193317409285"></a>Sets the file memory mapping attribute.</p> 200</td> 201</tr> 202<tr id="row178971473283"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p4898184782815"><a name="p4898184782815"></a><a name="p4898184782815"></a>LOS_IsRegionTypeDev</p> 203</td> 204<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p11898144722818"><a name="p11898144722818"></a><a name="p11898144722818"></a>Checks whether it is device memory mapping.</p> 205</td> 206</tr> 207<tr id="row11137546152811"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p20137194672812"><a name="p20137194672812"></a><a name="p20137194672812"></a>LOS_SetRegionTypeDev</p> 208</td> 209<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p81384462287"><a name="p81384462287"></a><a name="p81384462287"></a>Sets the device memory mapping attribute. </p> 210</td> 211</tr> 212<tr id="row1023564216285"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p92351842162819"><a name="p92351842162819"></a><a name="p92351842162819"></a>LOS_IsRegionTypeAnon</p> 213</td> 214<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p6235842132818"><a name="p6235842132818"></a><a name="p6235842132818"></a>Checks whether it is an anonymous mapping.</p> 215</td> 216</tr> 217<tr id="row1646364402813"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p44631644152814"><a name="p44631644152814"></a><a name="p44631644152814"></a>LOS_SetRegionTypeAnon</p> 218</td> 219<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p174631844182818"><a name="p174631844182818"></a><a name="p174631844182818"></a>Sets the anonymous mapping attribute. </p> 220</td> 221</tr> 222<tr id="row038233717288"><td class="cellrowborder" rowspan="5" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p6820331185317"><a name="p6820331185317"></a><a name="p6820331185317"></a>Verifying address</p> 223</td> 224<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p838383720282"><a name="p838383720282"></a><a name="p838383720282"></a>LOS_IsUserAddress</p> 225</td> 226<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p12383837102818"><a name="p12383837102818"></a><a name="p12383837102818"></a>Checks whether the address is in the user space.</p> 227</td> 228</tr> 229<tr id="row61506354284"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p2151113517288"><a name="p2151113517288"></a><a name="p2151113517288"></a>LOS_IsUserAddressRange</p> 230</td> 231<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p615123552814"><a name="p615123552814"></a><a name="p615123552814"></a>Checks whether the address region is in the user space.</p> 232</td> 233</tr> 234<tr id="row18301515194210"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p19301141519421"><a name="p19301141519421"></a><a name="p19301141519421"></a>LOS_IsKernelAddress</p> 235</td> 236<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p730110154427"><a name="p730110154427"></a><a name="p730110154427"></a>Checks whether the address is in the kernel space.</p> 237</td> 238</tr> 239<tr id="row191211718204213"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p1112121812423"><a name="p1112121812423"></a><a name="p1112121812423"></a>LOS_IsKernelAddressRange</p> 240</td> 241<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p6122101814219"><a name="p6122101814219"></a><a name="p6122101814219"></a>Checks whether the address region is in the kernel space.</p> 242</td> 243</tr> 244<tr id="row774964092115"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p17152102415416"><a name="p17152102415416"></a><a name="p17152102415416"></a>LOS_IsRangeInSpace</p> 245</td> 246<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p115218248547"><a name="p115218248547"></a><a name="p115218248547"></a>Checks whether the address region is in the process space.</p> 247</td> 248</tr> 249<tr id="row179196525521"><td class="cellrowborder" rowspan="3" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p153501191535"><a name="p153501191535"></a><a name="p153501191535"></a>vmalloc operations</p> 250</td> 251<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p152945155531"><a name="p152945155531"></a><a name="p152945155531"></a>LOS_VMalloc</p> 252</td> 253<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p1229461512535"><a name="p1229461512535"></a><a name="p1229461512535"></a>Requests memory using <strong id="b2981120154115"><a name="b2981120154115"></a><a name="b2981120154115"></a>vmalloc</strong>.</p> 254</td> 255</tr> 256<tr id="row1934135935211"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p162941115155315"><a name="p162941115155315"></a><a name="p162941115155315"></a>LOS_VFree</p> 257</td> 258<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p12294171516536"><a name="p12294171516536"></a><a name="p12294171516536"></a>Releases memory using <strong id="b1911793812416"><a name="b1911793812416"></a><a name="b1911793812416"></a>vmalloc</strong>.</p> 259</td> 260</tr> 261<tr id="row944214919304"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p644229163016"><a name="p644229163016"></a><a name="p644229163016"></a>LOS_IsVmallocAddress</p> 262</td> 263<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1344220993011"><a name="p1344220993011"></a><a name="p1344220993011"></a>Checks whether the address is requested by using <strong id="b11623210425"><a name="b11623210425"></a><a name="b11623210425"></a>vmalloc</strong>.</p> 264</td> 265</tr> 266<tr id="row72131845145315"><td class="cellrowborder" rowspan="4" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p84847816543"><a name="p84847816543"></a><a name="p84847816543"></a>Requesting memory</p> 267</td> 268<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p8787345546"><a name="p8787345546"></a><a name="p8787345546"></a>LOS_KernelMalloc</p> 269</td> 270<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p17787444543"><a name="p17787444543"></a><a name="p17787444543"></a>Requests memory less than 16 KiB from the heap memory pool; otherwise, requests multiple contiguous physical memory pages.</p> 271</td> 272</tr> 273<tr id="row48491549145311"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p14787149541"><a name="p14787149541"></a><a name="p14787149541"></a>LOS_KernelMallocAlign</p> 274</td> 275<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p478719411543"><a name="p478719411543"></a><a name="p478719411543"></a>Requests memory with alignment attributes according to the following rules: obtain memory less than 16 KiB from the heap memory pool; otherwise, request multiple contiguous physical memory pages.</p> 276</td> 277</tr> 278<tr id="row151093538536"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p15787134185412"><a name="p15787134185412"></a><a name="p15787134185412"></a>LOS_KernelFree</p> 279</td> 280<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p878712410546"><a name="p878712410546"></a><a name="p878712410546"></a>Releases kernel heap memory.</p> 281</td> 282</tr> 283<tr id="row5126856205319"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p197871646545"><a name="p197871646545"></a><a name="p197871646545"></a>LOS_KernelRealloc</p> 284</td> 285<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p378813416547"><a name="p378813416547"></a><a name="p378813416547"></a>Reallocates the kernel memory space.</p> 286</td> 287</tr> 288<tr id="row12397132718549"><td class="cellrowborder" rowspan="5" valign="top" width="12.811281128112812%" headers="mcps1.2.4.1.1 "><p id="p112971954115419"><a name="p112971954115419"></a><a name="p112971954115419"></a>Others</p> 289</td> 290<td class="cellrowborder" valign="top" width="29.84298429842984%" headers="mcps1.2.4.1.2 "><p id="p2777034145414"><a name="p2777034145414"></a><a name="p2777034145414"></a>LOS_PaddrQuery</p> 291</td> 292<td class="cellrowborder" valign="top" width="57.34573457345735%" headers="mcps1.2.4.1.3 "><p id="p13777834115413"><a name="p13777834115413"></a><a name="p13777834115413"></a>Obtains the physical IP address based on the virtual address.</p> 293</td> 294</tr> 295<tr id="row5558122119542"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p9558421155418"><a name="p9558421155418"></a><a name="p9558421155418"></a>LOS_VmSpaceFree</p> 296</td> 297<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p755852119545"><a name="p755852119545"></a><a name="p755852119545"></a>Releases the process space, including the virtual memory region and page table.</p> 298</td> 299</tr> 300<tr id="row15860142919544"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p168603298547"><a name="p168603298547"></a><a name="p168603298547"></a>LOS_VmSpaceReserve</p> 301</td> 302<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p12860429185410"><a name="p12860429185410"></a><a name="p12860429185410"></a>Reserves a memory space in the process space.</p> 303</td> 304</tr> 305<tr id="row394217543569"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p11943125419566"><a name="p11943125419566"></a><a name="p11943125419566"></a>LOS_VaddrToPaddrMmap</p> 306</td> 307<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p16943954105613"><a name="p16943954105613"></a><a name="p16943954105613"></a>Maps the physical address region with the specified length to a virtual address region. You need to request the physical address region before the operation.</p> 308</td> 309</tr> 310<tr id="row18527155718"><td class="cellrowborder" valign="top" headers="mcps1.2.4.1.1 "><p id="p118526110579"><a name="p118526110579"></a><a name="p118526110579"></a>LOS_UserSpaceVmAlloc</p> 311</td> 312<td class="cellrowborder" valign="top" headers="mcps1.2.4.1.2 "><p id="p1485214117575"><a name="p1485214117575"></a><a name="p1485214117575"></a>Requests an address region in the user process space based on information such as the address, size, and permission.</p> 313</td> 314</tr> 315</tbody> 316</table> 317 318### How to Develop<a name="section8752103914513"></a> 319 320To use APIs related to virtual memory: 321 3221. Obtain the process space structure using the APIs for obtaining the process space, and access the structure information. 3232. Perform the following operations on the virtual address region: 324 - Call **LOS\_RegionAlloc** to request a virtual address region. 325 326 - Call **LOS\_RegionFind** and **LOS\_RegionRangeFind** to check whether the corresponding address region exists. 327 - Call **LOS\_RegionFree** to release a virtual address region. 328 3293. Call **vmalloc** and memory requesting APIs to apply for memory in the kernel as required. 330 331> **NOTE:** 332>The physical memory requested by using the memory requesting APIs must be contiguous. If the system cannot provide a large number of contiguous memory blocks, the request fails. Therefore, the memory requesting APIs are recommended for requesting small memory blocks. Non-contiguous physical memory can be obtained by using **vmalloc**. However, the memory is allocated in the unit of pages \(4096 bytes/page in the current system\). If you want memory that is an integer multiple of a page, you can use **vmalloc**. For example, you can use **vmalloc** to request memory for file reading in a file system, which demands a large cache. 333 334
