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

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Message-ID: <a8e1da0806232249s36eb90c7la517a40ccfe839ea@mail.gmail.com>
Date:	Tue, 24 Jun 2008 13:49:48 +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 4:01 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 do some test about this last weekend, there's some questions,  could
you help to fix it?

1. MAXMEM :
 (-__PAGE_OFFSET - __VMALLOC_RESERVE).
The space after VMALLOC_END is included as well, seting it to
(VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE), is it right?

2. VMALLOC_OFFSET is not considered in __VMALLOC_RESERVE
Should fixed by adding VMALLOC_OFFSET to it.

3. VMALLOC_START :
 (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) & ~(VMALLOC_OFFSET - 1))
So it's not always 8M, bigger than 8M possible.
Set it to ((unsigned long)high_memory + VMALLOC_OFFSET), is it right?

Attached the proposed patch. please give some advice.

Regards
dave

Download attachment "diff.vmalloc" of type "application/octet-stream" (1949 bytes)