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SubjectRe: [PATCH 20/40] autonuma: alloc/free/init mm_autonuma
Hi Rik,

On Sun, Jul 01, 2012 at 11:33:17AM -0400, Rik van Riel wrote:
> On 06/28/2012 08:56 AM, Andrea Arcangeli wrote:
>
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 0adbe09..3e5a0d9 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -527,6 +527,8 @@ static void mm_init_aio(struct mm_struct *mm)
> >
> > static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
> > {
> > + if (unlikely(alloc_mm_autonuma(mm)))
> > + goto out_free_mm;
> > atomic_set(&mm->mm_users, 1);
> > atomic_set(&mm->mm_count, 1);
> > init_rwsem(&mm->mmap_sem);
>
> I wonder if it would be possible to defer the allocation
> of the mm_autonuma struct to knuma_scand, so short lived
> processes never have to allocate and free the mm_autonuma
> structure.
>
> That way we only have a function call at exit time, and
> the branch inside kfree that checks for a null pointer.

It would be possible to convert them to prepare_mm/task_autonuma (the
mm side especially would be a branch once in a while) but it would
then become impossible to inherit the mm/task stats across
fork/clone. Right now the default is to reset them, but two sysfs
switches control that, and I wouldn't drop those until I've the time
to experiment how large kernel builds are affected by enabling the
stats inheritance. Right now kernel builds are unaffected because of
the default stat-resetting behavior and gcc too quick to be measured.


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