linux-kernel - Re: Linux 2.6.24-rc7 Build-Failure at __you_cannot_kmalloc_that

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Message-ID: <Pine.LNX.4.64.0801071014450.22642@schroedinger.engr.sgi.com>
Date:	Mon, 7 Jan 2008 10:31:53 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	unlisted-recipients:; (no To-header on input)
cc:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bunk@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Andy Whitcroft <apw@...dowen.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: Linux 2.6.24-rc7 Build-Failure at __you_cannot_kmalloc_that_much

On Mon, 7 Jan 2008, Andrew Morton wrote:

> > : undefined reference to `__you_cannot_kmalloc_that_much'

There is also a kernel.org bugzilla for this at

http://bugzilla.kernel.org/show_bug.cgi?id=9669
For some reason my adds to this do not show up.

In both cases we have a 

k(z/m)alloc(sizeof(*pointer), ...)

that is for some reason failing. I guess what happens is that the function 
in which this occurs is too complex for gcc 3.2. Thus it stops constant 
folding the sizeof(*pointer) in the complex inline-if-cascade that SLAB 
needs to determine the cache and does not eliminate the 
__you_cannot_kmalloc_that_much branch().

SLUB in that case just puts a series of if comparisions in the code. This 
means compilation does not fail but a large amount of code is generated.

We could replace the __you_cannot_kmalloc_that_much() with a BUG() 
statement so we have the same effect in SLAB?

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