linux-kernel - Re: [PATCH] mem-hotplug: let memblock skip the hotpluggable memory regions in __next_mem

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Message-ID: <53EF6C79.3000603@huawei.com>
Date:	Sat, 16 Aug 2014 22:36:41 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"Wen Congyang" <wency@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"H. Peter Anvin" <hpa@...or.com>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mem-hotplug: let memblock skip the hotpluggable memory
 regions in __next_mem_range()

On 2014/8/16 21:04, Tejun Heo wrote:

> On Mon, Aug 11, 2014 at 09:31:22PM +0800, Xishi Qiu wrote:
>> Let memblock skip the hotpluggable memory regions in __next_mem_range(),
>> it is used to to prevent memblock from allocating hotpluggable memory 
>> for the kernel at early time. The code is the same as __next_mem_range_rev().
>>
>> Clear hotpluggable flag before releasing free pages to the buddy allocator.
> 
> Please try to explain "why" in addition to "what".  Why do we need to
> clear hotpluggable flag in free_low_memory_core_early() in addition to
> numa_clear_node_hotplug() in x86 numa.c?  Does this make x86 code
> redundant?  If not, why?
> 

Hi Tejun,

numa_clear_node_hotplug()? There is only numa_clear_kernel_node_hotplug().

If we don't clear hotpluggable flag in free_low_memory_core_early(), the 
memory which marked hotpluggable flag will not free to buddy allocator.
Because __next_mem_range() will skip them.

free_low_memory_core_early
	for_each_free_mem_range
		for_each_mem_range
			__next_mem_range		

Thanks,
Xishi Qiu

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