Subject: Re: Split pmap_activate() into pmap_activate() and pmap_newvmspace().
To: Chuck Silvers <>
From: Jason R Thorpe <>
List: tech-kern
Date: 09/07/2002 10:02:27
On Sat, Sep 07, 2002 at 09:39:23AM -0700, Chuck Silvers wrote:

 > how is operation 1 per-LWP?  the address space is the same for each LWP
 > in a process, so wouldn't they use the same ASN, etc?
 > if the PCB is going to be per-LWP, shouldn't there be a corresponding
 > structure that is per-proc, and wouldn't any address space information
 > be in that structure instead of in the PCB?

The "about to switch to a LWP that uses this address space" is a 
per-LWP operation.  I.e. "make sure this LWP's address space is ready
to go, because I'm about to use it".

 > (though I'd think that the per-LWP structure would be an LCB,
 > leaving "PCB" per-process.  it does stand for "process control block"
 > after all.)

Well, the PCB is part of u-area, which is a per-LWP thing.  There's
really nothing left in the PCB if you split it into LCB and PCB, so
it was a "don't make too many waves" kind of approach taken :-)

 > when would a process get a new address space while it has multiple LWPs?
 > the address space changing out from under an LWP would cause a lot of problems,
 > I'd think.  could you give an example of how this would work?

I don't have any real scenarios for this right now.  However, it was a
hole in the previous pmap interface specification, IMO.

See the diff I posted to tech-kern ... it might make things more clear.

        -- Jason R. Thorpe <>