linux-kernel - Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf

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Date:	Mon, 28 Apr 2014 17:31:22 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>
CC:	Christian Borntraeger <borntraeger@...ibm.com>,
	Avi Kivity <avi.kivity@...il.com>,
	Gleb Natapov <gleb@...nel.org>,
	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm
 async_pf_execute()

Il 28/04/2014 16:06, Andrea Arcangeli ha scritto:
>> >
>> > "task" is only used to increment task_struct->xxx_flt. I don't think
>> > async_pf_execute() actually needs this (current is PF_WQ_WORKER after
>> > all), but I didn't dare to do another change in the code I can hardly
>> > understand.
> Considering the faults would be randomly distributed among the kworker
> threads my preference would also be for NULL instead of current.
>
> ptrace and uprobes tends to be the only two places that look into
> other mm with gup, ptrace knows the exact pid that it is triggering
> the fault into, so it also can specify the correct task so the fault
> goes in the right task struct. uprobes uses NULL.

KVM knows the correct task (it was in current when kvm_create_vm was 
called), and doing accounting right would be nice.  But I agree that 
NULL is less misleading than a dummy current, and I applied patch 3 too.

Paolo
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