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authorhttps://me.yahoo.com/a/g3Ccalpj0NhN566pHbUl6i9QF0QEkrhlfPM-#b1c14 <diana@web>2015-02-16 20:08:03 +0100
committerGNU Hurd web pages engine <web-hurd@gnu.org>2015-02-16 20:08:03 +0100
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-[[!meta copyright="Copyright © 2013 Free Software Foundation, Inc."]]
-
-[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
-id="license" text="Permission is granted to copy, distribute and/or modify this
-document under the terms of the GNU Free Documentation License, Version 1.2 or
-any later version published by the Free Software Foundation; with no Invariant
-Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
-is included in the section entitled [[GNU Free Documentation
-License|/fdl]]."]]"""]]
-
-[[!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