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

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Message-ID: <52D538FD.8010907@ti.com>
Date:	Tue, 14 Jan 2014 15:17:49 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Philipp Hachtmann <phacht@...ux.vnet.ibm.com>,
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>
CC:	<linux-mm@...ck.org>, <qiuxishi@...wei.com>, <dhowells@...hat.com>,
	<daeseok.youn@...il.com>, <liuj97@...il.com>, <yinghai@...nel.org>,
	<zhangyanfei@...fujitsu.com>, <santosh.shilimkar@...com>,
	<tangchen@...fujitsu.com>
Subject: Re: [PATCH V3 2/2] mm/memblock: Add support for excluded memory areas

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.

Seems, it would be safer to track separately memory, available
for Linux ("memory" regions), and real phys memory. For example:
- add memblock type "phys_memory" and update it each time
 memblock_add()/memblock_remove() are called,
but don't update, if memblock_nomap()/memblock_remap() are called?

Another question is - Should the real phys memory configuration data be
a part of memblock or not?

Also, I like more memblock_steal()/memblock_reclaim() names for new APIs )

regards,
-grygorii
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