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

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Date:	Mon, 16 Jun 2008 16:52:16 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
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

On Mon, Jun 16, 2008 at 4:08 PM, Dave Young <hidave.darkstar@...il.com> wrote:
> On Mon, Jun 16, 2008 at 4:01 PM, Ingo Molnar <mingo@...e.hu> wrote:
>>
>> * 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.

I built with:
__VMALLOC_RESERVE = memparse(arg, &arg) + 2 * VMALLOC_OFFSET;

But it doesn't work, still oops at ie. vmalloc=4M (BUT vmalloc=8M is ok)
I can't figure out what's wrong with it.

Regards
dave
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