linux-kernel - Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap allocator

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Message-ID: <4A0D276B.4010703@kernel.org>
Date:	Fri, 15 May 2009 17:27:23 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	mingo@...e.hu, andi@...stfloor.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap			 allocator

Jan Beulich wrote:
>>>> Tejun Heo <tj@...nel.org> 15.05.09 10:11 >>>
>>>>> This would additionally address a potential problem on 32-bits -
>>>>> currently, for a 32-CPU system you consume half of the vmalloc space
>>>>> with PAE (on non-PAE you'd even exhaust it, but I think it's
>>>>> unreasonable to expect a system having 32 CPUs to not need PAE).
>>>> I recall having about the same conversation before.  Looking up...
>>>>
>>>> -- QUOTE --
>>>>  Actually, I've been looking at the numbers and I'm not sure if the
>>>>  concern is valid.  On x86_32, the practical number of maximum
>>>>  processors would be around 16 so it will end up 32M, which isn't
>>>>  nice and it would probably a good idea to introduce a parameter to
>>>>  select which allocator to use but still it's far from consuming all
>>>>  the VM area.  On x86_64, the vmalloc area is obscenely large at 245,
>>>>  ie 32 terabytes.  Even with 4096 processors, single chunk is measly
>>>>  0.02%.
>>> Just to note - there must be a reason we (SuSE/Novell) build our default
>>> 32-bit kernel with support for 128 CPUs, which now is simply broken.
>> It's not broken, it will just fall back to 4k allocator.  Also, please
> 
> I'm afraid I have to disagree: There's no check (not even in
> vm_area_register_early()) whether the vmalloc area is actually large enough
> to fulfill the request.

Hah... indeed.  Well, it's solved now.

Thanks.

-- 
tejun
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