linux-kernel - Re: [PATCH 15/16] mm: use vm_unmapped

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Message-Id: <20121106.124133.1287008316099748150.davem@davemloft.net>
Date:	Tue, 06 Nov 2012 12:41:33 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	riel@...hat.com
Cc:	walken@...gle.com, akpm@...ux-foundation.org, hughd@...gle.com,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	ralf@...ux-mips.org, lethal@...ux-sh.org, cmetcalf@...era.com,
	x86@...nel.org, wli@...omorphy.com, linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linux-sh@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH 15/16] mm: use vm_unmapped_area() on sparc32
 architecture

From: Rik van Riel <riel@...hat.com>
Date: Tue, 06 Nov 2012 02:30:07 -0500

> On 11/05/2012 08:25 PM, David Miller wrote:
>> From: Michel Lespinasse <walken@...gle.com>
>> Date: Mon,  5 Nov 2012 14:47:12 -0800
>>
>>> Update the sparc32 arch_get_unmapped_area function to make use of
>>> vm_unmapped_area() instead of implementing a brute force search.
>>>
>>> Signed-off-by: Michel Lespinasse <walken@...gle.com>
>>
>> Hmmm...
>>
>>> -	if (flags & MAP_SHARED)
>>> -		addr = COLOUR_ALIGN(addr);
>>> -	else
>>> -		addr = PAGE_ALIGN(addr);
>>
>> What part of vm_unmapped_area() is going to duplicate this special
>> aligning logic we need on sparc?
>>
> 
> That would be this part:
> 
> +found:
> + /* We found a suitable gap. Clip it with the original low_limit. */
> +	if (gap_start < info->low_limit)
> +		gap_start = info->low_limit;
> +
> +	/* Adjust gap address to the desired alignment */
> + gap_start += (info->align_offset - gap_start) & info->align_mask;
> +
> +	VM_BUG_ON(gap_start + info->length > info->high_limit);
> +	VM_BUG_ON(gap_start + info->length > gap_end);
> +	return gap_start;
> +}

Ok, now I understand.  Works for me:

Acked-by: David S. Miller <davem@...emloft.net>
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