linux-kernel - Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning

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Message-ID: <alpine.LFD.0.98.0706011653290.3957@woody.linux-foundation.org>
Date:	Fri, 1 Jun 2007 16:57:20 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Srinivasa Ds <srinivasa@...ibm.com>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dinakar Guniguntala <dino@...ibm.com>, pj@....com,
	simon.derr@...l.net, clameter@...ulhu.engr.sgi.com,
	rientjes@...gle.com
Subject: Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777
 warning



On Fri, 1 Jun 2007, Christoph Lameter wrote:
> 
> A too large alloc is >32MB or MAX_ORDER << PAGE_SIZE. A BUG_ON in 
> kmalloc_slab() will trigger.

Did we use to BUG_ON()? I think that's wrong. There are ways for users to 
potentially ask the kernel to do big allocations, and the correct response 
is to say "no can do", not to crash!

> Here is the updated patch. It works fine here:
> 
> SLUB: Return BADPTR instead of warning for kmalloc(0)

Looks fine to me. My only comment is that

> -	if (!x)
> +	if (!x || x == BADPTR)
>  		return;

This could be micro-optimized (again, non-standard, but it should be 
"practically portable") to have just a single test using something like

	if ((unsigned long)x <= 16)
		return;

but I guess it doesn't really matter much.

I think this is better than what we have now, but I also suspect it's 
*not* something we should try this late in the -rc sequence ;)

Andrew, want to take this patch to -mm to see if it triggers anything?

		Linus
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