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

From: David Rientjes
Date: Fri Oct 19 2012 - 05:31:27 EST

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.
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