linux-kernel - Re: [Patch v4 01/12] memory-hotplug: try to offline the memory twice to avoid dependence

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Message-ID: <50BDBFAA.7040008@cn.fujitsu.com>
Date:	Tue, 04 Dec 2012 17:17:30 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Wen Congyang <wency@...fujitsu.com>
CC:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Jiang Liu <liuj97@...il.com>, Len Brown <len.brown@...el.com>,
	benh@...nel.crashing.org, paulus@...ba.org,
	Christoph Lameter <cl@...ux.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Jianguo Wu <wujianguo@...wei.com>
Subject: Re: [Patch v4 01/12] memory-hotplug: try to offline the memory twice
 to avoid dependence

On 11/27/2012 06:00 PM, Wen Congyang wrote:
> memory can't be offlined when CONFIG_MEMCG is selected.
> For example: there is a memory device on node 1. The address range
> is [1G, 1.5G). You will find 4 new directories memory8, memory9, memory10,
> and memory11 under the directory /sys/devices/system/memory/.
>
> If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup
> when we online pages. When we online memory8, the memory stored page cgroup
> is not provided by this memory device. But when we online memory9, the memory
> stored page cgroup may be provided by memory8. So we can't offline memory8
> now. We should offline the memory in the reversed order.
>
> When the memory device is hotremoved, we will auto offline memory provided
> by this memory device. But we don't know which memory is onlined first, so
> offlining memory may fail. In such case, iterate twice to offline the memory.
> 1st iterate: offline every non primary memory block.
> 2nd iterate: offline primary (i.e. first added) memory block.
>
> This idea is suggested by KOSAKI Motohiro.
>
> CC: David Rientjes<rientjes@...gle.com>
> CC: Jiang Liu<liuj97@...il.com>
> CC: Len Brown<len.brown@...el.com>
> CC: Christoph Lameter<cl@...ux.com>
> Cc: Minchan Kim<minchan.kim@...il.com>
> CC: Andrew Morton<akpm@...ux-foundation.org>
> CC: KOSAKI Motohiro<kosaki.motohiro@...fujitsu.com>
> CC: Yasuaki Ishimatsu<isimatu.yasuaki@...fujitsu.com>
> Signed-off-by: Wen Congyang<wency@...fujitsu.com>

Reviewed-by: Tang Chen <tangchen@...fujitsu.com>

> ---
>   mm/memory_hotplug.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e4eeaca..b825dbc 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1012,10 +1012,13 @@ int remove_memory(u64 start, u64 size)
>   	unsigned long start_pfn, end_pfn;
>   	unsigned long pfn, section_nr;
>   	int ret;
> +	int return_on_error = 0;
> +	int retry = 0;
>
>   	start_pfn = PFN_DOWN(start);
>   	end_pfn = start_pfn + PFN_DOWN(size);
>
> +repeat:
>   	for (pfn = start_pfn; pfn<  end_pfn; pfn += PAGES_PER_SECTION) {
>   		section_nr = pfn_to_section_nr(pfn);
>   		if (!present_section_nr(section_nr))
> @@ -1034,14 +1037,23 @@ int remove_memory(u64 start, u64 size)
>
>   		ret = offline_memory_block(mem);
>   		if (ret) {
> -			kobject_put(&mem->dev.kobj);
> -			return ret;
> +			if (return_on_error) {
> +				kobject_put(&mem->dev.kobj);
> +				return ret;
> +			} else {
> +				retry = 1;
> +			}
>   		}
>   	}
>
>   	if (mem)
>   		kobject_put(&mem->dev.kobj);
>
> +	if (retry) {
> +		return_on_error = 1;
> +		goto repeat;
> +	}
> +
>   	return 0;
>   }
>   #else

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