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

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Date:	Tue, 06 Nov 2012 02:30:07 -0500
From:	Rik van Riel <riel@...hat.com>
To:	David Miller <davem@...emloft.net>
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

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;
+}
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