On 10/19/2012 01:31 PM, David Rientjes wrote:

On Fri, 19 Oct 2012, Glauber Costa wrote:

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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.

Well, I thought about it.

And I personally don't like it. I think all kthreads should be treated
the same. We have control over it, unlike any userspace application. We
never expect its memory consumption to explode.

Specially considering that those allocations are supposed to be
short-lived, we are only paying the res_counters count for no reason.

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