Subversion Repositories HelenOS-doc

        <title>Address spaces and areas</title>

        <title>Address space areas</title>

        <para>- adresovy prostor se sklada z tzv. address space areas

               flag indicates code execution permission. Some architectures do not support execution persmission restriction. In this case this flag has no effect.

        usporadanych v B+stromu; tyto areas popisuji vyuzivane casti

              <emphasis>AS_AREA_DEVICE</emphasis>

        adresoveho prostoru patrici do user address space. Kazda cast je dana

               marks area as mapped to the device memory.

        svoji bazovou adresou, velikosti a flagy (rwx/dd).</para>

          </itemizedlist></para>

        <para>- uzivatelske thready maji moznost manipulovat se svym adresovym

        <para>Kernel provides possibility tasks create/expand/shrink/share its

        prostorem (vytvaret/resizovat/sdilet) as_areas pomoci syscallu</para>

        address space via the set of syscalls.</para>

        <para>- nektery hardware umoznuje rozlisit ruzne adresove prostory od

        <para>When switching to the different task, kernel also require to

        sebe (cilem je maximalizovat vyuziti TLB); dela to tak, ze s kazdou

        switch mappings to the different address space. In case TLB cannot

        polozkou TLB/strankovacich tabulek sdruzi identifikator adresoveho

        distinguish address space mappings, all mappings from the old address

        prostoru (ASID, RID, ppc32 ???). Tyto id mivaji ruznou sirku: 8-bitu

        space should be flushed, which can create certain uncessary

        az 24-bitu (kolik ma ppc32?)</para>

        overhead.</para>

        <para>- kernel tomu rozumi a sam pouziva abstrakci ASIDu (na ia64 to

        <para>To avoid this, some architectures have capability to segregate

        je napr. cislo odvozene od RIDu, na mips32 to je ASID samotny);

        different address spaces on HW level introducing the ASID (address

        existence ASIDu je nutnou podminkou pouziti _global_ page hash table

        space identifier, that tells to which address space this record is

        mechanismu.</para>

        applicable.</para>

        <para>- na vsech arch. plati, ze asidu je mnohem mene, nez teoreticky

        <para>HelenOS kernel can take advantage of this hardware supported

        pocet soucasne bezicich tasku ~ adresovych prostoru, takze je

        identifier by having an ASID abstraction which is connected to the

        implementovan mechanismus, ktery umoznuje jednomu adresovemu prostoru

        corresponding architecture identifier. I.e. on ia64 kernel ASID is

        ASID odebrat a pridelit ho jinemu</para>

        actually the hardware identifier.</para>

        <para>- vztah task ~ adresovy prostor: teoreticky existuje moznost, ze

        <para>Due to the hardware limitations ASID has limited length from 8

        je adresovy prostor sdilen vice tasky, avsak tuto moznost nepouzivame

        unique address space identifier for all tasks running in the system.

        a neni ani nijak osetrena. Tim padem plati, ze kazdy task ma vlastni

        In such situations special ASID stealing algoritm is used, which takes

        adresovy prostor</para>

        ASID from inactive task and assigns it to the active task.</para>

          genericke hash table s oddelenymi collision chains</para>

          genericke hash table s oddelenymi collision chains. ASID support is

        <title>Translation Lookaside buffer</title>

        <title>Translation Lookaside Buffer</title>

        algoritmu</para>

        algoritm</para>

        blocks in the list i<mathphrase> </mathphrase>(i.e. buddies), the

        blocks in the list i<mathphrase />(i.e. buddies), the buddy allocator

        buddy allocator would coalesce them and put the resulting block in

        would coalesce them and put the resulting block in list <mathphrase>i

        list <mathphrase>i + 1</mathphrase>, provided that the resulting block

        + 1</mathphrase>, provided that the resulting block would be naturally

        would be naturally aligned. Similarily, when the allocator is asked to

        aligned. Similarily, when the allocator is asked to allocate a block

        <mathphrase>2<superscript>i</superscript></mathphrase>, it first tries

        of size <mathphrase>2<superscript>i</superscript></mathphrase>, it

        to satisfy the request from the list with index i. If the request

        first tries to satisfy the request from the list with index i. If the

        cannot be satisfied (i.e. the list i is empty), the buddy allocator

        request cannot be satisfied (i.e. the list i is empty), the buddy

        will try to allocate and split a larger block from the list with index

        allocator will try to allocate and split a larger block from the list

        i + 1. Both of these algorithms are recursive. The recursion ends

        with index i + 1. Both of these algorithms are recursive. The

        either when there are no blocks to coalesce in the former case or when

        recursion ends either when there are no blocks to coalesce in the

        there are no blocks that can be split in the latter case.</para>

        former case or when there are no blocks that can be split in the

          <para>Another important entity of magazine layer is a full magazine

          <para>Another important entity of magazine layer is the common full

          depot, that stores full magazines which are used by any of the CPU

          may be used by any of the CPU magazine caches to reload active CPU

          magazine caches to reload active CPU magazine. Magazine depot can be

          magazine. This list of magazines can be pre-filled with full

          pre-filled with full magazines during initialization, but in current

          magazines during initialization, but in current implementation it is

          implementation it is filled during object deallocation, when CPU

          filled during object deallocation, when CPU magazine becomes

          magazine becomes full.</para>

          full.</para>