linux-kernel - Re: More problems in setup_pcpu

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Message-ID: <49D44251.4000606@kernel.org>
Date:	Thu, 02 Apr 2009 13:42:57 +0900
From:	Tejun Heo <tj@...nel.org>
To:	David Miller <davem@...emloft.net>
CC:	linux-kernel@...r.kernel.org
Subject: Re: More problems in setup_pcpu_remap()

Hello,

David Miller wrote:
> The way this code is currently designed, it can exhaust all of the
> VMALLOC address space on both x86 and x86_64, and then some.
> 
> It allocates PMD_SIZE * num_possible_cpus() of vmalloc space.
> 
> PMD_SIZE is 2MB, num_possible_cpus() can be up to 4096....
> which can easily exceed (VMALLOC_END - VMALLOC_START)
> 
> Initially I had set out to implement sparc64 support for the new
> per-cpu stuff, but it looks like I'm stuck finding bugs in the x86
> implementation instead :-)

Eh... sorry about that.  :-)

I guess we'll have to put a cap on how high possible cpus can be for
remap allocator.  e.g. if single chunk size is over 20% of the whole
vmalloc area, don't use remap.  Does anyone have a good random %
number on mind?

Thanks.

-- 
tejun
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