Date: Tue, 11 Nov 2003 10:24:46 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: "Martin J. Bligh" <mbligh@aracnet.com>
cc: Erik Jacobson <erikj@subway.americas.sgi.com>,
       <linux-kernel@vger.kernel.org>
Subject: Re: 2.6 /proc/interrupts fails on systems with many CPUs
In-Reply-To: <9710000.1068573723@flay>
Message-ID: <Pine.LNX.4.44.0311111019210.30657-100000@home.osdl.org>
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On Tue, 11 Nov 2003, Martin J. Bligh wrote:
> 
> I think it'd make more sense to only use vmalloc when it's explicitly 
> too big for kmalloc - or simply switch on num_online_cpus > 100 or 
> whatever a sensible cutoff is (ie nobody but you would ever see this ;-))

No, please please please don't do these things.

vmalloc() is NOT SOMETHING YOU SHOULD EVER USE! It's only valid for when
you _need_ a big array, and you don't have any choice. It's slow, and it's
a very restricted resource: it's a global resource that is literally
restricted to a few tens of megabytes. It should be _very_ carefully used.

There are basically no valid new uses of it. There's a few valid legacy
users (I think the file descriptor array), and there are some drivers that
use it (which is crap, but drivers are drivers), and it's _really_ valid
only for modules. Nothing else.

Basically: if you think you need more memory than a kmalloc() can give,
you need to re-organize your data structures. To either not need a big 
area, or to be able to allocate it in chunks.

		Linus

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