linux-kernel - Re: [PATCH 8/8] KVM: PPC: Add hugepage support for IOMMU in-kernel handling

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Date:	Wed, 10 Jul 2013 12:42:04 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alexey Kardashevskiy <aik@...abs.ru>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 8/8] KVM: PPC: Add hugepage support for IOMMU in-kernel handling


On 10.07.2013, at 12:40, Alexander Graf wrote:

> 
> On 10.07.2013, at 12:39, Benjamin Herrenschmidt wrote:
> 
>> On Wed, 2013-07-10 at 12:33 +0200, Alexander Graf wrote:
>>> 
>>> It's not exactly obvious that you're calling it with writing == 1 :).
>>> Can you create a new local variable "is_write" in the calling
>>> function, set that to 1 before the call to get_user_pages_fast and
>>> pass it in instead of the 1? The compiler should easily optimize all
>>> of that away, but it makes the code by far easier to read.
>> 
>> Ugh ?
>> 
>> Nobody else does that .... (look at futex :-)
> 
> Yeah, that's fortunately code that I don't have to read :).

The "proper" alternative would be to pass an enum for read/write into the function rather than an int. But that'd be a pretty controversial, big change that I'd rather not put on Alexey. With a local variable we're nicely self-contained readable ;)


Alex

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