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Message-ID: <563AC8C0.40007@inspur.com>
Date: Thu, 5 Nov 2015 11:10:56 +0800
From: Changsheng Liu <liuchangsheng@...pur.com>
To: Dave Hansen <dave.hansen@...el.com>, <akpm@...ux-foundation.org>,
<isimatu.yasuaki@...fujitsu.com>, <vbabka@...e.cz>,
<yasu.isimatu@...il.com>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
<wunan@...pur.com>, <yanxiaofeng@...pur.com>, <fandd@...pur.com>,
Wang Nan <wangnan0@...wei.com>,
Yinghai Lu <yinghai@...nel.org>,
Tang Chen <tangchen@...fujitsu.com>,
Toshi Kani <toshi.kani@...com>, Xishi Qiu <qiuxishi@...wei.com>
Subject: Re: [PATCH V8] mm: memory hot-add: hot-added memory can not be added
to movable zone by default
在 2015/11/5 0:31, Dave Hansen 写道:
> On 11/04/2015 12:23 AM, liuchangsheng wrote:
>> After the user config CONFIG_MOVABLE_NODE,
>> When the memory is hot added, should_add_memory_movable() return 0
>> because all zones including ZONE_MOVABLE are empty,
>> so the memory that was hot added will be assigned to ZONE_NORMAL,
>> and we need using the udev rules to online the memory automatically:
>> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline",
>> ATTR{state}="online_movable"
>> The memory block onlined by udev must be adjacent to ZONE_MOVABLE.
>> The events of memory section are notified to udev asynchronously,
>> so it can not ensure that the memory block onlined by udev is
>> adjacent to ZONE_MOVABLE.So it can't ensure memory online always success.
>> But we want the whole node to be added to ZONE_MOVABLE by default.
> I'm still a bit confused about the whole scenario here.
>
> Is the core problem:
> 1. We add memory in a new node and that node can not be made entirely
> movable?
As I know, System will not ensure that the node can be made
entirely movable if the memory of
the node is assigned to ZONE_NORMAL
> or
> 2. We add memory to an existing zone that has some non-movable memory
> and we want the new memory to be movable?
It will work if we want to let the memroy movable by using
movable_node
>
>> @@ -1201,6 +1201,9 @@ static int check_hotplug_memory_range(u64 start, u64 size)
>> /*
>> * If movable zone has already been setup, newly added memory should be check.
>> * If its address is higher than movable zone, it should be added as movable.
>> + * And if system boots up with movable_node and config CONFIG_MOVABLE_NOD and
>> + * added memory does not overlap the zone before MOVABLE_ZONE,
>> + * the memory is added as movable.
>> * Without this check, movable zone may overlap with other zone.
>> */
> This comment is describing what the code does, but is rather sparse on
> why. This scenario is pretty convoluted and I can barely make sense of
> why it is doing this today while looking at the whole changelog, much
> less in a few years when the original changelog will be harder to come by.
>
> Also please put the comment next to the new if() statement. It's really
> hard to match the comment to the code the way you have it now.
>
>> static int should_add_memory_movable(int nid, u64 start, u64 size)
>> @@ -1208,6 +1211,10 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
>> unsigned long start_pfn = start >> PAGE_SHIFT;
>> pg_data_t *pgdat = NODE_DATA(nid);
>> struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
>> + struct zone *pre_zone = pgdat->node_zones + (ZONE_MOVABLE - 1);
>> +
>> + if (movable_node_is_enabled() && (zone_end_pfn(pre_zone) <= start_pfn))
>> + return 1;
>>
>> if (zone_is_empty(movable_zone))
>> return 0;
>>
> .
>
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