linux-kernel - Re: [PATCH V3 2/2] mm/memblock: Add support for excluded memory areas

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Date:	Tue, 14 Jan 2014 09:24:49 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Philipp Hachtmann <phacht@...ux.vnet.ibm.com>
CC:	Grygorii Strashko <grygorii.strashko@...com>,
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <qiuxishi@...wei.com>, <dhowells@...hat.com>,
	<daeseok.youn@...il.com>, <liuj97@...il.com>, <yinghai@...nel.org>,
	<zhangyanfei@...fujitsu.com>, <tangchen@...fujitsu.com>
Subject: Re: [PATCH V3 2/2] mm/memblock: Add support for excluded memory areas

On Tuesday 14 January 2014 08:17 AM, Grygorii Strashko wrote:
> Hi Philipp,
> 
> On 01/13/2014 03:03 PM, Philipp Hachtmann wrote:
>> Add a new memory state "nomap" to memblock. This can be used to truncate
>> the usable memory in the system without forgetting about what is really
>> installed.
> 
> 
> Sorry, but this solution looks a bit complex (and probably wrong - from design point of view))
> if you need just to fix memblock_start_of_DRAM()/memblock_end_of_DRAM() APIs.
> 
> More over, other arches use at least below APIs: 
> - memblock_is_region_memory() !!!
> - for_each_memblock(memory, reg) !!!
> - __next_mem_pfn_range() !!!
> - memblock_phys_mem_size()
> - memblock_mem_size()
> - memblock_start_of_DRAM()
> - memblock_end_of_DRAM()
> with assumption that "memory" regions array have been updated
> when mem block is stolen (no-mapped), as result this change may
> have unpredictable side effects :( if these new APIs
> will be re-used (for ARM arch, as example).
> 
> You can take a look on how ARM is using arm_memblock_steal() - 
> the stolen memory is not accounted any more.
> 
I was also wondering instead of nomap state, the memblock_add/remove()
will do the same trick. arm_memblock_steal() wrapper does achieve
similar functionality of reserving the DRAM without mapping it into
the Linux. Why not just use the same idea ?

Regards,
Santosh


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