Re: Query regarding Copy-on-write

[Simon Valiquette <v.simon@ieee.org>]

Jagadeesh Bhaskar P a écrit :
> Hi again,
>   I got the concept. I had no problem understanding the explanation...I
> already knew the concepts of virtual memory and paging so that was not a
> problem.
> 
>   According to ur reply, after the sharing, will always the range of
> addresses generated by the process, ie the virtual addresses be the same
> of the parent, even if the physical memory pointed to by that is
> different.
> 

   Yes, otherwise the pointers would point to the wrong adresses and the 
program will probably quickly segfault.

>   So basically, is it that sharing VM imply that the range of addresses
> is shared, and physical pages pointed to by them may or maynot be the
> same?
> 

   The range of virtual addresses is reused, not shared, but I guess it 
is just a question of using the good words (you are probably also a 
non-native english speakers).  But yes that's the basic idea.

> Please do help, and thanks for the previous elaborate explanation!
> 

   When I first looked inside the Linux kernel, I started by trying to 
understand how it handled memory.  I finally realized how crazy I was, 
and switched to an easier part.  But by the time, I had learned quite a 
lot about VM, and also made a minimalist OS for a MC68000 microcontroler 
(only basic process support without even support for a filesystem). 
That's also probably why I don't think the actual kernel support 
copy-on-write on MMU-less processor, as I can't think of any good and 
efficient implementation for that.


Simon Valiquette

---
The memory management on the PowerPC can be used
to frighten small children.
   - Linus Torvalds

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