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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
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