Re: linux page table

[Jiri Kosina]

On Sun, 2 Sep 2012, Xin Tong wrote:

> >> 3. can two different processes have their CR3 being the same value
> >> even though they have different first level page tables ?
> >
> > Yes, if they are created by clone(CLONE_VM). In such case they share the
> > same mm_struct, and therefore mm_struct->pgd (which is exactly what is
> > loaded into cr3 in switch_mm()) is the same.
> >
> 
> Is this the COW mechanism in linux. what if the cloned process need to
> have set of its own pages later. do the CR3s for the 2 processes
> become different at that point ?

That is a different story. COW is applied on fork() (i.e. spawning new 
process), not on clone(CLONE_VM) (i.e. spawning new thread).

-- 
Jiri Kosina
SUSE Labs
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