[Devel] Re: [PATCH v5 06/14] memcg: kmem controller infrastructure

[David Rientjes]

On Fri, 19 Oct 2012, Glauber Costa wrote:

> >>> Do we actually need to test PF_KTHREAD when current->mm == NULL? 
> >>> Perhaps because of aio threads whcih temporarily adopt a userspace mm?
> >>
> >> I believe so. I remember I discussed this in the past with David
> >> Rientjes and he advised me to test for both.
> >>
> > 
> > PF_KTHREAD can do use_mm() to assume an ->mm but hopefully they aren't 
> > allocating slab while doing so.  Have you considered actually charging 
> > current->mm->owner for that memory, though, since the kthread will have 
> > freed the memory before unuse_mm() or otherwise have charged it on behalf 
> > of a user process, i.e. only exempting PF_KTHREAD?
> > 
> I always charge current->mm->owner.
> 

Yeah, I'm asking have you considered charging current->mm->owner for the 
memory when a kthread (current) assumes the mm of a user process via 
use_mm()?  It may free the memory before calling unuse_mm(), but it's also 
allocating the memory on behalf of a user so this exemption might be 
dangerous if use_mm() becomes more popular.  I don't think there's 
anything that prevents that charge, I'm just wondering if you considered 
doing it even for kthreads with an mm.