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6b3fd2fecb
Update documentation/comments to rename addr, fun, var, stmt, blk, desc, reg, seg, ptr, dup, clus, val, and bttn, to address, function, variable, statement, block, description, register, segment, pointer, duplicate, cluster, value, and button, respectively.
121 lines
13 KiB
HTML
Executable file
121 lines
13 KiB
HTML
Executable file
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<pre style="font-family:monospace;font-size:12pt">
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<a name="l1"></a><span class=cF5> Memory Overview</span><span class=cF0>
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<a name="l2"></a>
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<a name="l3"></a>Paging is practically not used. 64-bit mode requires paging, however, so it is identity-mapped -- virtual identical to
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<a name="l4"></a>physical. All tasks on all cores use the same page table map, just as though all addresses are physical addresses. 2Meg or
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<a name="l5"></a>1Gig page table entries are used. Nothing swaps to disk.
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<a name="l6"></a>
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<a name="l7"></a>In ZealOS, the lowest 2Gig of memory is called the </span><span class=cF2>code heap</span><span class=cF0>. ZealOS's compiler always uses 32-bit signed relative JMP & CALL
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<a name="l8"></a>insts because 64-bit CALLs take two insts. With signed +/- 32-bit values, code can only call a function within 2Gig distance.
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<a name="l9"></a> Therefore, ZealOS keeps all code in the lowest 2Gig memory addresses including what would normally be called "the kernel".
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<a name="l10"></a>Two Gig is plenty for code, don't worry.
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<a name="l11"></a>
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<a name="l12"></a>You can create new, independent heaps using </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/HeapCtrl.CC.html#l1"><span class=cF4>HeapCtrlInit</span></a><span class=cF0>(). Then, use the </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l3567"><span class=cF4>CHeapCtrl</span></a><span class=cF0> as the 2nd arg to </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l391"><span class=cF4>MAlloc</span></a><span class=cF0>(). See </span><a href="https://zeal-operating-system.github.io/ZealOS/System/Utils/HeapLog.CC.html#l83"><span class=cF4>HeapLog</span></a><span class=cF0>()
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<a name="l13"></a>for an example.
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<a name="l14"></a>
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<a name="l15"></a>Memory alloced by a task will be freed when the task is killed. The </span><a href="https://zeal-operating-system.github.io/ZealOS/Doc/Glossary.DD.html#l154"><span class=cF4>System Task</span></a><span class=cF0> is a task that never dies. His memory is like
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<a name="l16"></a>kernel memory in other operating systems. See </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l408"><span class=cF4>SysCAlloc</span></a><span class=cF0>(), </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l394"><span class=cF4>SysMAlloc</span></a><span class=cF0>(), </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l427"><span class=cF4>SysMAllocIdent</span></a><span class=cF0>() and </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l503"><span class=cF4>SysStrNew</span></a><span class=cF0>().
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<a name="l17"></a>
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<a name="l18"></a>All of the regular page tables are marked, "cached". When accessing hardware, however, you need uncached page table. The
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<a name="l19"></a>lowest 4Gig addresses have an alias to access hardware located toward the top of mapped space, </span><span class=cF2>0x01D7800000</span><span class=cF0>. See </span><span class=cF4>
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<a name="l20"></a></span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/MultiProc.CC.html#l147"><span class=cF4>dev.uncached_alias</span></a><span class=cF0>.
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<a name="l21"></a>
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<a name="l22"></a>During an extended powered-on session of ZealOS, in theory, memory will become fragmented, requiring a reboot. It has never
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<a name="l23"></a>happens to me.
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<a name="l24"></a>
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<a name="l25"></a>See </span><a href="https://zeal-operating-system.github.io/ZealOS/System/Utils/MemRep.CC.html#l219"><span class=cF4>MemRep</span></a><span class=cF0>() and </span><a href="https://zeal-operating-system.github.io/ZealOS/Demo/MemDemo.CC.html#l1"><span class=cF4>::/Demo/MemDemo.CC</span></a><span class=cF0>.
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<a name="l26"></a>
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<a name="l27"></a>
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<a name="l28"></a></span><span class=cF5> Single System-wide Memory Map
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<a name="l29"></a>
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<a name="l30"></a></span><span class=cF2> 0x0000007C00- 0x0000036BEF</span><span class=cF0>
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<a name="l31"></a> Kernel module, placed here by the boot-loader, </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l4484"><span class=cF4>BOOT_RAM_BASE</span></a><span class=cF0>.
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<a name="l32"></a>
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<a name="l33"></a></span><span class=cF2> 0x0000096600- 0x0000096FFF</span><span class=cF0>
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<a name="l34"></a> Boot block relocated here before loading the Kernel module, </span><a href="https://zeal-operating-system.github.io/ZealOS/System/Boot/BootDVD.CC.html#l1"><span class=cF4>BootDVD</span></a><span class=cF0> & </span><a href="https://zeal-operating-system.github.io/ZealOS/System/Boot/BootHD.CC.html#l1"><span class=cF4>BootHD</span></a><span class=cF0>.
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<a name="l35"></a>
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<a name="l36"></a></span><span class=cF2> 0x0000097000- 0x0000097030</span><span class=cF0> Multicore start-up vect code, </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l665"><span class=cF4>MPN_VECT</span></a><span class=cF0>.
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<a name="l37"></a></span><span class=cF2>~0x000009F000- 0x000009FFFF</span><span class=cF0> Extended BIOS data area.
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<a name="l38"></a></span><span class=cF2> 0x00000A0000- 0x00000BFFFF</span><span class=cF0> VGA graphics mem with alias at </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KGlobals.CC.html#l30"><span class=cF4>text</span></a><span class=cF0>.vga_alias.
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<a name="l39"></a></span><span class=cF2> 0x0000100000- 0x0000101FFF</span><span class=cF0> </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l4127"><span class=cF4>CSysFixedArea</span></a><span class=cF0> for misc.
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<a name="l40"></a></span><span class=cF2> 0x0000110000- 0x007FFFFFFF</span><span class=cF0> Code Heap mem.
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<a name="l41"></a>
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<a name="l42"></a></span><span class=cF2> 0x00E0000000- 0x00FFFFFFFF</span><span class=cF0>
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<a name="l43"></a> 32-bit devices could alloc memory at 0xF0000000 going up, but this is wrong, since some PCs already have devices at
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<a name="l44"></a> 0xF0000000. PCI devices are supported, so </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MemPhysical.CC.html#l64"><span class=cF4>Mem32DevAlloc</span></a><span class=cF0>() flaws could become an issue.
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<a name="l45"></a>
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<a name="l46"></a></span><span class=cF2> 0x0080000000-~0x00DFFFFFFF</span><span class=cF0>
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<a name="l47"></a></span><span class=cF2> 0x0100000000-~0x01D77FFFFF</span><span class=cF0>
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<a name="l48"></a> Data Heap mem. (The physical memory that exists in this range is data heap.)
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<a name="l49"></a>
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<a name="l50"></a></span><span class=cF2> 0x01D7800000- 0x02D77FFFFF</span><span class=cF0>
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<a name="l51"></a> Uncached alias of first 4Gig. (For 32-bit device access.)
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<a name="l52"></a>
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<a name="l53"></a></span><span class=cF2> - 0x02D77FFFFF</span><span class=cF0>
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<a name="l54"></a> 64-bit devices are alloced with </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MemPhysical.CC.html#l122"><span class=cF4>Mem64DevAlloc</span></a><span class=cF0>() counting backward.
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<a name="l55"></a>
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<a name="l56"></a>
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<a name="l57"></a>
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<a name="l58"></a>* Note: There is a break in the data-heap block pool. This has no effect except the obvious effect that fragmentation has on
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<a name="l59"></a>contiguous requests. You can </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l391"><span class=cF4>MAlloc</span></a><span class=cF0>() an 8Gig chunk on a 12Gig machine. You can </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MAllocFree.CC.html#l391"><span class=cF4>MAlloc</span></a><span class=cF0>() a 32Gig chunk on a 64Gig machine.
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<a name="l60"></a>
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<a name="l61"></a>* Note: For systems with less than 2Gig RAM, the code and data heap block pools are the same. For systems with 2-4Gig of RAM,
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<a name="l62"></a>the code heap is 1/4 of the total. See </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/BlkPool.CC.html#l31"><span class=cF4>BlkPoolsInit</span></a><span class=cF0>().
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<a name="l63"></a>
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<a name="l64"></a>
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<a name="l65"></a></span><span class=cF5> History</span><span class=cF0>
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<a name="l66"></a>
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<a name="l67"></a>In 2003, Terry Davis wanted to make a no-paging ring-0-only 64-bit operating system for super speed with simplicity and full
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<a name="l68"></a>access. With paging, every memory request requires 5 accesses -- it must access the address itself, 4K, 2Meg, 1Gig, and 512Gig
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<a name="l69"></a>page tables, but the CPU's translation look-aside buffer mostly removes the penalty for using paging. So, he did not want to
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<a name="l70"></a>use paging, but long mode requires it. He did the next best thing -- he identity-mapped everything and achieved the
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<a name="l71"></a>simplicity he was after with subtle performance boosts, not wasting time changing address maps. We look forward to the day
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<a name="l72"></a>Intel makes an optimized no-paging long mode.
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<a name="l73"></a>
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<a name="l74"></a>Terry needed VGA A0000-BFFFF memory to be write-through and 0xE0000000-0xFFFFFFFF to be uncached for various devices. All
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<a name="l75"></a>64-bit computers allow stopping address translation at 2Meg page size, not using 4K. He wanted to use 2Meg for everything
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<a name="l76"></a>because it's faster, with one less level of page tables. He had to make A0000-BFFFF write-through, though, so he could not
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<a name="l77"></a>use 2Meg size on the lowest page. He did the lowest 2Meg area as 4K pages. He also unmapped the first 4K to cause a fault
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<a name="l78"></a>when dereferencing NULL.
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<a name="l79"></a>
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<a name="l80"></a>In 2016, Terry came-up with an alternate idea. He double mapped the lowest memory with an alias that was uncached. Accessing
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<a name="l81"></a>the lowest 2Meg area directly was cached but the alias he created up at the top of address space was uncached. See </span><span class=cF4>
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<a name="l82"></a></span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MemPhysical.CC.html#l157"><span class=cF4>UncachedAliasAlloc</span></a><span class=cF0>(). Unfortunately, he could no longer boast of the simplicity of identity mapping everything. Since many
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<a name="l83"></a>of the users are familiar with A0000-BFFFF, it is actually pretty seriously unfortunate that they cannot use the
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<a name="l84"></a>easy-to-understand numbers of A0000-BFFFF, but must access the relocated alias location. See </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KMain.CC.html#l113"><span class=cF4>text.vga_alias</span></a><span class=cF0>. We also no
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<a name="l85"></a>longer cause a fault when dereferencing NULL.
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<a name="l86"></a>
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<a name="l87"></a>Then, Terry switched to 1Gig page sizes. For the lowest 4Gig, he set-up an alias up at the top of address space. See </span><span class=cF4>
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<a name="l88"></a></span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/Memory/MemPhysical.CC.html#l157"><span class=cF4>UncachedAliasAlloc</span></a><span class=cF0>(). Not all computers support 1Gig page tables, however, so he also supported 2Meg.
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<a name="l89"></a>
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<a name="l90"></a>Terry's original plan was to allow changing the page tables as needed, so he had code for taking control of 2Meg pages and
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<a name="l91"></a>marking them uncached or whatever. When he did an HDAudio driver, he requested some 32-bit address space as uncached. Today,
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<a name="l92"></a>all of the first 4Gig can be accessed without caching at the </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/MultiProc.CC.html#l147"><span class=cF4>dev.uncached_alias</span></a><span class=cF0>.
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</span></pre></body>
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