linux-kernel - Re: More problems in setup_pcpu

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Message-Id: <20090401.215233.134215150.davem@davemloft.net>
Date:	Wed, 01 Apr 2009 21:52:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tj@...nel.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: More problems in setup_pcpu_remap()

From: Tejun Heo <tj@...nel.org>
Date: Thu, 02 Apr 2009 13:42:57 +0900

> 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?

I would suggest instead to rethink what this code is doing.

It would make more sense to carve up 2MB chunks into some-power-of-2
pieces and use that as the unit size.

You could retain the NUMA goals of this function, as well as the
ability to be using 2MB pages in the TLBs.

And consider that if the dynamic allocation part of this code triggers
even once, you'll end up eating twice as much VMALLOC space.

Using 2MB per cpu is just rediculious, and really not even necessary.
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