Linux Memory Management Documentation

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1、MMDOC.LinuxMemoryManagementDocumentation•Abstract•IntroductionoAoverviewoftheMMsystemoVarioustermsusedinLinux•MMSub-Systeminitialization.oMemorycategorizationoPagingstartoStartPagingoBootmemHandlingoPagetablesetup°paging_init()°pagetable_init()°free_area_init()•Aboutthisdocument...AbstractT

2、hisdocumentaimsatdocumentingtheLinuxV2.4.18MemoryManagementsubsystemforthei386architecture.Thisiplantodobygivingabriefdescriptionofthealgorithmsusedformemorymanagement,andexplanationtobitsandpiecesofcodefromthelinuxkernelwhereeverneeded.Itdoesnottalkabouthighmemyet.Thisdocumentdoesnotaimtob

3、eacodecomentry,buttriestoexplainthelogicandalgorithmthatgoesbehindthecode.Assuchthisdocumenttriestominimizethelearningcurve(thatihad)whiletryingtounderstandthelinuxkernelIntroductionMemorymanagementsystemis,thepartoftheoperatingsystemkernelthatmanagesthePhysicalmemory.Apartfromthatitalsodoe

4、smanythingslikeprovidingthe,•Physicalpagestovariouslayersofthememorymanagementsystem.•Contiguouskernelmemoryusingaslaballocator.•Non-contiguousmemoryusingthevmallocalgorithm•user-spaceprocesseswithVirtualmemory.Someknowledgeabouttheix86pagingmechanismwillbehelpfull(ithinkmandatory)toproceed

5、withthisdocument.IhaveseenalotofgooddocumentsfromIntel,thatarereallyusefull.Iwilltrytolinktheminthebibliography.Itisnotnecessarytoenablepagingandsegmentationinix86architecture.Butenablingthemprovideslotoffunctionalitylikesegmentwiseprotectionandvirtualmemory.Sopagingisenabledlinuxandisdonei

6、ntheearlybootprocessitself.AoverviewoftheMMsystemItishelpfulltohaveaoveralltheoreticalviewofthesystembeforewedoanyrealanalysisofcodeoralgorithm.Firstwewillseeaboutthevarioustypesofmemoryaddressesusedbythekernel.•Physicaladdress ‐ Thememoryasknownbythelow‐levelhardware.•Direct‐mappedkernelvi

7、rtualaddress ‐ Thephysicaladdressappliedanoffset.(Thisalsoisdifferentinsomearchitectures).•Purekernelvirtualaddress ‐ Theaddressthatcanbedereferencedbythekernel,butwhichdoesnotmapintophysicaladdressdirectly.i.e.,cannotdereferencedjustbyoffsettingasinthec