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

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Date:	Thu, 5 Dec 2013 18:48:21 +0000
From:	"Strashko, Grygorii" <grygorii.strashko@...com>
To:	Tejun Heo <tj@...nel.org>
CC:	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	"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

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.

Regards,
-grygorii--
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