linux-kernel - Re: [PATCH v2] memory-hotplug: add sysfs zones_online

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Date:	Mon, 25 Aug 2014 09:55:27 +0800
From:	Zhang Zhen <zhenzhang.zhang@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Toshi Kani <toshi.kani@...com>,
	Dave Hansen <dave.hansen@...el.com>,
	"David Rientjes" <rientjes@...gle.com>,
	<isimatu.yasuaki@...fujitsu.com>, <n-horiguchi@...jp.nec.com>,
	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] memory-hotplug: add sysfs zones_online_to attribute

On 2014/8/23 6:16, Andrew Morton wrote:
> On Mon, 18 Aug 2014 11:25:36 +0800 Zhang Zhen <zhenzhang.zhang@...wei.com> wrote:
> 
>> On 2014/8/16 5:37, Toshi Kani wrote:
>>> On Wed, 2014-08-13 at 12:10 +0800, Zhang Zhen wrote:
>>>> Currently memory-hotplug has two limits:
>>>> 1. If the memory block is in ZONE_NORMAL, you can change it to
>>>> ZONE_MOVABLE, but this memory block must be adjacent to ZONE_MOVABLE.
>>>> 2. If the memory block is in ZONE_MOVABLE, you can change it to
>>>> ZONE_NORMAL, but this memory block must be adjacent to ZONE_NORMAL.
>>>>
>>>> With this patch, we can easy to know a memory block can be onlined to
>>>> which zone, and don't need to know the above two limits.
>>>>
>>>> Updated the related Documentation.
>>>>
>>>> Change v1 -> v2:
>>>> - optimize the implementation following Dave Hansen's suggestion
>>>>
>>>> Signed-off-by: Zhang Zhen <zhenzhang.zhang@...wei.com>
>>>> ---
>>>>  Documentation/ABI/testing/sysfs-devices-memory |  8 ++++
>>>>  Documentation/memory-hotplug.txt               |  4 +-
>>>>  drivers/base/memory.c                          | 62 ++++++++++++++++++++++++++
>>>>  include/linux/memory_hotplug.h                 |  1 +
>>>>  mm/memory_hotplug.c                            |  2 +-
>>>>  5 files changed, 75 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
>>>> index 7405de2..2b2a1d7 100644
>>>> --- a/Documentation/ABI/testing/sysfs-devices-memory
>>>> +++ b/Documentation/ABI/testing/sysfs-devices-memory
>>>> @@ -61,6 +61,14 @@ Users:		hotplug memory remove tools
>>>>  		http://www.ibm.com/developerworks/wikis/display/LinuxP/powerpc-utils
>>>>
>>>>
>>>> +What:           /sys/devices/system/memory/memoryX/zones_online_to
>>>
>>> I think this name is a bit confusing.  How about "valid_online_types"?
>>>
>> Thanks for your suggestion.
>>
>> This patch has been added to -mm tree.
>> If most people think so, i would like to modify the interface name.
>> If not, let's leave it as it is.
> 
> Yes, the name could be better.  Do we actually need "online" in there? 
> How about "valid_zones"?

Ok, i will change it to valid_zones.
> 
> Also, it's not really clear to me why we need this sysfs file at all. 
> Do people really read sysfs files, make onlining decisions and manually
> type in commands?  Or is this stuff all automated?  If the latter then
> the script can take care of all this?  For example, attempt to online
> the memory into the desired zone and report failure if that didn't
> succeed?

Just like Dave Hansen says, the scripts should be changed when we add a new
zone type. And ZONE_MOVABLE may be missed by the scripts writer.
> 
> IOW, please update the changelog to show
> 
> a) example output from
>    /sys/devices/system/memory/memoryX/whatever-we-call-it and
> 
> b) example use-cases which help reviewers understand why this
>    feature will be valuable to users.

Sorry, this patch has been added to -next tree. I can't modify the changelog.
> 
> Also, please do address the error which Yasuaki Ishimatsu identified.
> 
Yeah, i have been waiting for http://ozlabs.org/~akpm/mmots/broken-out/memory-hotplug-add-sysfs-zones_online_to-attribute-fix-2.patch
added to -mm tree.
So i can send a patch based on -mm tree to address the error which Yasuaki Ishimatsu identified.
Otherwise, conflicts may occur.

Thanks!
> 
> .
> 


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