Re: mmaping on plan9? (was Re: [9fans] venti /plan9port mmapped

[ori@eigenstate.org]

Quoth Bakul Shah via 9fans <9fans@9fans.net>:
> 
> No idea how horrible a hack is needed to implement such a thing or even if it is possible at all but I had to share this ;-)
> 

pretty horrible; so, we hard-code up to 10 segments in the kernel,
which allows things to be really simple; when N is 10, O(n) is fine.

We've got a ton of loops doing things like:

        for(i = 0; i < NSEG; i++)

and it works great; the simplicity of our VM system also means that
our fork is something like 10 times faster than fork on Unix, and

If you want to start having a lot of small maps, you start to need
complex data structures to track them and look them up quickly on
page fault; things start to suck.

In addition to mmap being superficially easy, but hard to use correctly,
and very hard to use correctly in the case of trying to write with it,
I think it's best to leave it behind.


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