linux-kernel - Re: [PATCH] kernel parameter vmalloc size fix

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Message-ID: <20080616080131.GC25632@elte.hu>
Date:	Mon, 16 Jun 2008 10:01:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, hpa@...or.com,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] kernel parameter vmalloc size fix


* Dave Young <hidave.darkstar@...il.com> wrote:

> booting kernel with vmalloc=[any size<=16m] will oops.
> 
> It's due to the vm area hole.
> 
> In include/asm-x86/pgtable_32.h:
> #define VMALLOC_OFFSET	(8 * 1024 * 1024)
> #define VMALLOC_START	(((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) \
> 			 & ~(VMALLOC_OFFSET - 1))
> 
> BUG_ON in arch/x86/mm/init_32.c will be triggered:
> BUG_ON((unsigned long)high_memory		> VMALLOC_START);
> 
> Fixed by return -EINVAL for invalid parameter

hm. Why dont we instead add the size of the hole to the 
__VMALLOC_RESERVE value instead? There's nothing inherently bad about 
using vmalloc=16m. The VM area hole is really a kernel-internal 
abstraction that should not be visible in the usage of the parameter.

	Ingo
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