linux-kernel - Re: [kernel] powerpc: Make vmalloc_to

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Message-ID: <56A83728.4090601@ozlabs.ru>
Date:	Wed, 27 Jan 2016 14:19:04 +1100
From:	Alexey Kardashevskiy <aik@...abs.ru>
To:	Paul Mackerras <paulus@...abs.org>,
	Michael Ellerman <mpe@...erman.id.au>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [kernel] powerpc: Make vmalloc_to_phys() public

On 01/25/2016 09:06 PM, Paul Mackerras wrote:
> On Mon, Jan 25, 2016 at 04:46:03PM +1100, Michael Ellerman wrote:
>> On Thu, 2016-21-01 at 07:35:08 UTC, Alexey Kardashevskiy wrote:
>>> This makes vmalloc_to_phys() public as there will be another user
>>> (in-kernel VFIO acceleration) for it soon.
>>>
>>> As a part of future little optimization, this changes the helper to call
>>> vmalloc_to_pfn() instead of vmalloc_to_page() as the size of the
>>> struct page may not be power-of-two aligned which will make gcc use
>>> multiply instructions instead of shifts.
>>
>> You should also mention why you need to export it, presumably because whatever
>> new user you have in mind can be built as a module.
>
> If I remember correctly, it's the *existing* user in hv-24x7.c that
> needs the export.

No, CONFIG_HV_PERF_CTRS (which controls hv-24x7.c) is "bool" so today 
hv-24x7.c cannot compile as a module.

This exports the vmalloc_to_phys() symbol as a new user is going to be KVM 
which can compile as a module.


-- 
Alexey