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# IRC, freenode, #hurd, 2012-02-01

    <sekon> on Hurd what is the difference between kernel memory object and
      pmap module ??
    <sekon> pmap is heap/libraries table for each thread while kernel memory
      object refers to arbitary blobs of data ??
    <braunr> sekon: pmap is the low level memory mapping module
    <braunr> i.e. it programs the mmu
    <braunr> and these aren't hurd-specific, they are mach modules
    <sekon> braunr: so kernel memonry objects consists of a bunch of pmaps ??
    <braunr> sekon: memory objects can be various things, be specific please
    <braunr> (they're certainly not a bunch of pmaps though, no)
    <braunr> there is one pmap per vm_map, and there is one vm_map per task
    <braunr> and there is no need for double question marks, is ther ??
    <sekon> lol then is kernel memory object , please excuse the metaphor
      something like a base class for pmap 
    <braunr> i don't know what a "kernel memory object" is, be specific please,
      again
    <sekon> braunr:
      http://courses.cs.vt.edu/~cs5204/fall05-gback/presentations/MachOS_Rajesh.ppt 
    <sekon> goto page titled External Memory Management (EMM) on page 15 
    <sekon> Kernel memory object shows up 
    <braunr> you know there are other formats for this document
    <sekon> nope .. i did not know that 
    <sekon> in page 17 pmamp shows up 
    <braunr> "the problems of external memory management" ?
    <sekon> braunr: the paper i am also reading is called x15mach_thesis 
    <braunr> ah, that's mine
    * sekon bows 
    <sekon> :) 
    <braunr> ok i see page 17
    <sekon> so please good sir explain the relationship between kernel memory
      object and pmap 
    <sekon> (if any) 
    <sekon> braunr: there is no mention of kernel  memory object 
    <braunr> again, i don't see any reference or definition of "kernel memory
      object"
    <sekon> but your paper says 
    <sekon> that when page faults occur 
    <sekon> the kernel contact the manager for a kernel reference object 
    <sekon> *memory 
    <braunr> where ?
    <sekon> in section 2.1.3 (unless i read it wrong) 
    <sekon> no just a sec 
    <sekon> 2.1.5 
    <braunr> i never used the expression "kernel memory object" there :p
    <braunr> anyway, you're referring simple to memory objects as seen by
      userspace pagers
    <braunr> a memory object is a data container
    <braunr> usually, it's a file
    <braunr> but it can be anything
    <braunr> the pager is the task that provides its content and implements the
      object methods
    <braunr> as for the relation between them and the pmap module, it's a
      distant one
    <braunr> i'll explain it with an example
    <braunr> page fault -> request content of memory object at a given offset
      with given length from pager -> ask pmap to establish the mapping in the
      mmu
    <sekon> braunr: thank you ver much 
    <sekon> *very