linux-kernel - Re: [PATCH] kmalloc: Return NULL instead of link failure

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Message-ID: <497F8172.7000403@cs.helsinki.fi>
Date:	Tue, 27 Jan 2009 23:49:38 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jeff Mahoney <jeffm@...e.com>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] kmalloc: Return NULL instead of link failure

Andrew Morton wrote:
> On Tue, 20 Jan 2009 10:53:26 -0500
> Jeff Mahoney <jeffm@...e.com> wrote:
> 
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>>  The SLAB kmalloc with a constant value isn't consistent with the other
>>  implementations because it bails out with __you_cannot_kmalloc_that_much
>>  rather than returning NULL and properly allowing the caller to fall back
>>  to vmalloc or take other action. This doesn't happen with a non-constant
>>  value or with SLOB or SLUB.
>>
>>  Starting with 2.6.28, I've been seeing build failures on s390x. This is
>>  due to init_section_page_cgroup trying to allocate 2.5MB when the max
>>  size for a kmalloc on s390x is 2MB.
>>
>>  It's failing because the value is constant. The workarounds at the call
>>  size are ugly and the caller shouldn't have to change behavior depending
>>  on what the backend of the API is.
>>
>>  So, this patch eliminates the link failure and returns NULL like the
>>  other implementations.
>>
> 
> OK by me, is that's what the other sl[abcd...xyz]b.c implementations
> do.
> 
> That __you_cannot_kmalloc_that_much() thing has frequently been a PITA
> anyway - some gcc versions flub the constant_p() test and end up
> referencing __you_cannot_kmalloc_that_much() when the callsite was
> passing a variable `size' arg.

[snip]

> Strange patch format, but it applied.
> 
> I'll punt this patch in the Pekka direction.

Applied, thanks!

		Pekka
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