linux-kernel - Re: [PATCH v2 08/23] mm/memblock: Add memblock memory allocation apis

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Message-ID: <52A0E357.7090008@ti.com>
Date:	Thu, 5 Dec 2013 15:34:31 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	"Strashko, Grygorii" <grygorii.strashko@...com>
CC:	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 08/23] mm/memblock: Add memblock memory allocation
 apis

Grygorii,

On Thursday 05 December 2013 01:48 PM, Strashko, Grygorii wrote:
> Hi Tejun,
> 
>> On Thu, Dec 05, 2013 at 06:35:00PM +0200, Grygorii Strashko wrote:
>>>>> +#define memblock_virt_alloc_align(x, align) \
>>>>> +  memblock_virt_alloc_try_nid(x, align, BOOTMEM_LOW_LIMIT, \
>>>>> +                               BOOTMEM_ALLOC_ACCESSIBLE, MAX_NUMNODES)
>>>>
>>>> Also, do we really need this align variant separate when the caller
>>>> can simply specify 0 for the default?
>>>
>>> Unfortunately Yes.
>>> We need it to keep compatibility with bootmem/nobootmem
>>> which don't handle 0 as default align value.
>>
>> Hmm... why wouldn't just interpreting 0 to SMP_CACHE_BYTES in the
>> memblock_virt*() function work?
>>
> 
> Problem is not with memblock_virt*(). The issue will happen in case if
> memblock or nobootmem are disabled in below code (memblock_virt*() is disabled).
> 
> +/* Fall back to all the existing bootmem APIs */
> +#define memblock_virt_alloc(x) \
> +       __alloc_bootmem(x, SMP_CACHE_BYTES, BOOTMEM_LOW_LIMIT)
> 
> which will be transformed to 
> +/* Fall back to all the existing bootmem APIs */
> +#define memblock_virt_alloc(x, align) \
> +       __alloc_bootmem(x, align, BOOTMEM_LOW_LIMIT)
> 
> and used as
> 
> memblock_virt_alloc(size, 0);
> 
> so, by default bootmem code will use 0 as default alignment and not SMP_CACHE_BYTES
> and that is wrong.
> 
Looks like you didn't understood the suggestion completely.
The fall back inline will look like below .....

static inline memblock_virt_alloc(x, align)
{
	if (align == 0)
		align = SMP_CACHE_BYTES
	__alloc_bootmem(x, align, BOOTMEM_LOW_LIMIT);
}

regards,
Santosh


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