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[[!tag open_issue_gnumach]]


# IRC, freenode, #hurd, 2013-04-02

    <psockali> hi again, maybe someone has some metrics 
    <psockali> is mprotect / munprotect faster in hurd then in linux ?
    <pinotree> ?
    <psockali> can i protected a memory page against write access in hurd 
    <psockali> and if so, is it a fast operation ?
    <youpi> you can, I never measured, but it's probably the same cost as in
      linux
    <youpi> I don't see why it would be different, as it boils down to the same
      x86 trick
    <psockali> but i suppose it is part of the mach kernel doing the protection
      and not part of the unix layer ?
    <youpi> it is
    <youpi> the unix layer doesn't have mm control
    <youpi> it has to ask the kernel
    <braunr> it's slower on mach, as it's less optimized because of historical
      reasons
    <braunr> but that's about it
    <youpi> less optimized, how so?
    <braunr> well, more entry fragmentation
    <youpi> in the end you mark the page table and flush the tlb
    <braunr> yes
    <braunr> the high level virtual memory layer is a bit slower
    <youpi> but fragmentation doesn't come into play it you just have one
      memory object, does it?
    <braunr> it does, as it's about memory areas, not objects
    <braunr> the object is merely a backing store
    <braunr> protection, inheritance, copy on write are all area (vm_map_entry)
      attributes
    <braunr> also, some operations affect all the address spaces where a
      physical page is mapped
    <braunr> although i think linux does the same thing as mach/bsd now
    <youpi> but mprotect/munprotect doesn't, does it?
    <braunr> no
    <braunr> or perhaps by side effect, in some situations, i'm not sure
    <braunr> i think it depends if the memory is shared between processes, but
      i don't remember the details and can't think of a proper example right
      now
    <braunr> but anyway, "slower" here is negligible unless address spaces are
      really huge and filled with lots of map entries
    <braunr> psockali: why do you ask ?
    <psockali> can i post a link here ?
    <braunr> about what ?
    <psockali> it's regarding azul / managed runtime initiative 
    <psockali> a GC for java
    <braunr> why not
    <braunr> although i don't see the point for now :)
    <psockali> they have a custom MM management module for their GC as linux
      kernel modul
    <psockali> and i was wondering if mach would be any faster then linux in
      that aspect
    <psockali>
      http://stackoverflow.com/questions/3358545/whats-actually-in-the-managed-runtime-initiatives-kernel-patches-and-jvm
    <braunr> psockali: generally speaking, mach is slower than linux because of
      its age and the fact it didn't receive as much attention and
      microoptimization as linux did
    <braunr> psockali: about this article, there is no reason mach would be
      faster