Re: [RFC PATCH 5/5] refresh VM committed space after a task migration

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Tue, 2008-06-10 at 01:33 +0200, Andrea Righi wrote:
> +       preempt_disable();
> +       committed = atomic_long_read(&p->vm_committed_space);
> +       atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space);
> +       atomic_long_add(committed, &mem->vmacct.vm_committed_space);
> +       preempt_enable();
>  out:
>         mmput(mm);
>  }

Why bother with the preempt stuff here?  What does the actually protect
against?  I assume that you're trying to keep other tasks that might run
on this CPU from seeing weird, inconsistent numbers in here.  Is there
some other looks that keeps *other* cpus from seeing this?

In any case, I think it needs a big, fat comment.

-- Dave