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Date: Tue, 4 Nov 2014 16:46:32 +0800
From: Tang Chen <tangchen@...fujitsu.com>
To: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
<akpm@...ux-foundation.org>, <santosh.shilimkar@...com>,
<grygorii.strashko@...com>, <yinghai@...nel.org>,
<isimatu.yasuaki@...fujitsu.co>, <fabf@...net.be>,
<nzimmer@....com>, <wangnan0@...wei.com>, <vdavydov@...allels.com>,
<toshi.kani@...com>, <phacht@...ux.vnet.ibm.com>, <tj@...nel.org>,
<kirill.shutemov@...ux.intel.com>, <riel@...hat.com>,
<luto@...capital.net>, <hpa@...ux.intel.com>,
<aarcange@...hat.com>, <qiuxishi@...wei.com>, <mgorman@...e.de>,
<rientjes@...gle.com>, <hannes@...xchg.org>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
Gu Zheng <guz.fnst@...fujitsu.com>, <tangchen@...fujitsu.com>
Subject: Re: [PATCH 2/2] mem-hotplug: Fix wrong check for zone->pageset initialization
in online_pages().
On 11/04/2014 04:10 PM, Yasuaki Ishimatsu wrote:
> (2014/10/31 18:46), Tang Chen wrote:
>> When we are doing memory hot-add, the following functions are called:
>>
>> add_memory()
>> |--> hotadd_new_pgdat()
>> |--> free_area_init_node()
>> |--> free_area_init_core()
>> |--> zone->present_pages = realsize; /* 1. zone is populated */
>> |--> zone_pcp_init()
>> |--> zone->pageset = &boot_pageset; /* 2. zone->pageset is set to boot_pageset */
>>
>> There are two problems here:
>> 1. Zones could be populated before any memory is onlined.
>> 2. All the zones on a newly added node have the same pageset pointing to boot_pageset.
>>
>> The above two problems will result in the following problem:
>> When we online memory on one node, e.g node2, the following code is executed:
>>
>> online_pages()
>> {
>> ......
>> if (!populated_zone(zone)) {
>> need_zonelists_rebuild = 1;
>> build_all_zonelists(NULL, zone);
>> }
>> ......
>> }
>>
>> Because of problem 1, the zone has been populated, and the build_all_zonelists()
>> will never called. zone->pageset won't be updated.
>> Because of problem 2, All the zones on a newly added node have the same pageset
>> pointing to boot_pageset.
>> And as a result, when we online memory on node2, node3's meminfo will corrupt.
>> Pages on node2 may be freed to node3.
>>
>> # for ((i = 2048; i < 2064; i++)); do echo online_movable > /sys/devices/system/node/node2/memory$i/state; done
>> # cat /sys/devices/system/node/node2/meminfo
>> Node 2 MemTotal: 33554432 kB
>> Node 2 MemFree: 33549092 kB
>> Node 2 MemUsed: 5340 kB
>> ......
>> # cat /sys/devices/system/node/node3/meminfo
>> Node 3 MemTotal: 0 kB
>> Node 3 MemFree: 248 kB /* corrupted */
>> Node 3 MemUsed: 0 kB
>> ......
>>
>> We have to populate some zones before onlining memory, otherwise no memory could be onlined.
>> So when onlining pages, we should also check if zone->pageset is pointing to boot_pageset.
>>
>> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
>> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
>> ---
>> include/linux/mm.h | 1 +
>> mm/memory_hotplug.c | 6 +++++-
>> mm/page_alloc.c | 5 +++++
>> 3 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 02d11ee..83e6505 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1732,6 +1732,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...);
>>
>> extern void setup_per_cpu_pageset(void);
>>
>> +extern bool zone_pcp_initialized(struct zone *zone);
>> extern void zone_pcp_update(struct zone *zone);
>> extern void zone_pcp_reset(struct zone *zone);
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 3ab01b2..bc0de0f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1013,9 +1013,13 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>> * If this zone is not populated, then it is not in zonelist.
>> * This means the page allocator ignores this zone.
>> * So, zonelist must be updated after online.
>> + *
>> + * If this zone is populated, zone->pageset could be initialized
>> + * to boot_pageset for the first time a node is added. If so,
>> + * zone->pageset should be allocated.
>> */
>> mutex_lock(&zonelists_mutex);
>> - if (!populated_zone(zone)) {
>> + if (!populated_zone(zone) || !zone_pcp_initialized(zone)) {
>> need_zonelists_rebuild = 1;
>> build_all_zonelists(NULL, zone);
>> }
> Why does zone->present_pages of the hot-added memroy have valid value?
> In my understading, the present_pages is incremented/decremented by memory
> online/offline. So when hot adding memory, the zone->present_pages of the
> memory should be 0.
Before zone->managed_pages was introduced, zone->present_pages had been
abused.
It had two meaning:
1. pages existing in the zone
2. pages managed by buddy system in the zone
So, zone->managed_pages was introduced. Now, it looks like:
1. zone->present_pages is the pages existing in the zone
2. zone->managed_pages is the pages managed by buddy system
So when hot adding memory, the zone->present_pages should not be 0.
zone->managed_pages should be 0. And here, since zone->managed_pages
is updated in online_pages_range() callback, I think we should remove
zone->present_pages and node_present_pages updates from online_pages().
Furthermore, since we can online pages or online_movable pages,
zones in a node could be changed. So we should update zone->present_pages
when pfn is moved left or right.
Thanks.
>
> Thanks,
> Yasuaki Ishimatsu
>
>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 736d8e1..4ff1540 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6456,6 +6456,11 @@ void __meminit zone_pcp_update(struct zone *zone)
>> }
>> #endif
>>
>> +bool zone_pcp_initialized(struct zone *zone)
>> +{
>> + return (zone->pageset != &boot_pageset);
>> +}
>> +
>> void zone_pcp_reset(struct zone *zone)
>> {
>> unsigned long flags;
>>
>
> .
>
--
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