Re: Interprocess shared memory .... but file backed?

[Christopher Quinn <cq@htec.demon.co.uk>]

Mark Hahn wrote:

>>>well MAP_PRIVATE is "dont share" so not with that 8)
>>>Use MAP_SHARED and you'll get what you want
>>>
>>Certainly true! But MAP_SHARED gives uncontrolled flush of 
>>dirty data - so that's out for me. I only want 'privacy' to 
>>extend to the right to make changes permanent at my own 
>>discretion.
>>
> 
> right, and that's not what Unix provides.  in particular, mmap
> is a means for apps to be polite, not for them to strongarm
> the kernel.  in particular, if you mmap a file, much of the point
> is that the kernel chooses how much of the state is in ram or 
> on disk.  you can, of course, msync, or even munmap.
> 
> 
> 

Seems a bit restrictive to me. After all Unix is not an 
ossified standard! :)
Assuming clone() actually page table shares the vm covered 
by a mmap(MAP_PRIVATE) in the way I want, it isn't much to 
ask to be more *restrictive* on sharing?

So far, it's looking as if my ideal is unattainable with the 
current kernel.
Anyone disagree?


-- 
rgrds,
Chris Quinn