linux-kernel - Re: SLUB: Return ZERO_SIZE

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Date:	Mon, 4 Jun 2007 11:05:19 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, jeremy@...p.org
Subject: Re: SLUB: Return ZERO_SIZE_PTR for kmalloc(0)

On Mon, Jun 04, 2007 at 10:50:41AM -0700, Linus Torvalds wrote:
> The exception is if you use the memory allocator as a "ID allocator", but 
> quite frankly, if you use a size of zero, it's your own damn problem. 
> Insane code is not an argument for insane behaviour.
> If people can't be bothered to create a "random ID generator" themselves, 
> they had damn well better use "kmalloc(1)" rather than "kmalloc(0)" to get 
> a unique cookie. Asking the allocator to do something idiotic because some 
> idiot thinks a memory allocator is a cookie allocator is just crazy.

It's not such a great idea in general. Maybe it's a dumb device to cut
down on lines of code for merging or some such.


On Mon, Jun 04, 2007 at 10:50:41AM -0700, Linus Torvalds wrote:
> I can understand that things like user-level libraries have to take crazy 
> people into account, but the kernel internal libraries definitely do not.
> (Right now we warn once for zero-sized allocations anyway, and all the 
> cases we've found so far are either bugs that would have been found with 
> ZERO_ALLOC_PTR or would have been perfectly fine with it, so I don't think 
> anybody really _is_ that insane in the kernel)

There are always drivers for that, but I doubt any were sufficiently
creative to pick up on this. At least I've not see any.


-- wli
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