Re: [PATCH 1/3] memory_hotplug: fix stale node_states[N_NORMAL_MEMORY]

[Lai Jiangshan]

On 09/27/2012 10:32 PM, Ni zhan Chen wrote:
> On 09/27/2012 02:47 PM, Lai Jiangshan wrote:
>> Currently memory_hotplug only manages the node_states[N_HIGH_MEMORY],
>> it forgets to manage node_states[N_NORMAL_MEMORY]. it causes
>> node_states[N_NORMAL_MEMORY] becomes stale.
>>
>> We add check_nodemasks_changes_online() and check_nodemasks_changes_offline()
>> to detect whether node_states[N_HIGH_MEMORY] and node_states[N_NORMAL_MEMORY]
>> are changed while hotpluging.
>>
>> Also add @status_change_nid_normal to struct memory_notify, thus
>> the memory hotplug callbacks know whether the node_states[N_NORMAL_MEMORY]
>> are changed.
> 
> I still don't understand why need care N_NORMAL_MEMORY here, could you explain
> in details?

Hi, Chen

In short node_states[N_NORMAL_MEMORY] will become wrong in some situation.
many memory management code access to this node_states[N_NORMAL_MEMORY].

I will add more detail in the changelog in next round.

Thanks,
Lai

> 
>>
>> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
>> ---
>>   Documentation/memory-hotplug.txt |    5 ++-
>>   include/linux/memory.h           |    1 +
>>   mm/memory_hotplug.c              |   94 +++++++++++++++++++++++++++++++------
>>   3 files changed, 83 insertions(+), 17 deletions(-)
>>
>> diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
>> index 6d0c251..6e6cbc7 100644
>> --- a/Documentation/memory-hotplug.txt
>> +++ b/Documentation/memory-hotplug.txt
>> @@ -377,15 +377,18 @@ The third argument is passed by pointer of struct memory_notify.
>>   struct memory_notify {
>>          unsigned long start_pfn;
>>          unsigned long nr_pages;
>> +       int status_change_nid_normal;
>>          int status_change_nid;
>>   }
>>     start_pfn is start_pfn of online/offline memory.
>>   nr_pages is # of pages of online/offline memory.
>> +status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
>> +is (will be) set/clear, if this is -1, then nodemask status is not changed.
>>   status_change_nid is set node id when N_HIGH_MEMORY of nodemask is (will be)
>>   set/clear. It means a new(memoryless) node gets new memory by online and a
>>   node loses all memory. If this is -1, then nodemask status is not changed.
>> -If status_changed_nid >= 0, callback should create/discard structures for the
>> +If status_changed_nid* >= 0, callback should create/discard structures for the
>>   node if necessary.
>>     --------------
>> diff --git a/include/linux/memory.h b/include/linux/memory.h
>> index ff9a9f8..a09216d 100644
>> --- a/include/linux/memory.h
>> +++ b/include/linux/memory.h
>> @@ -53,6 +53,7 @@ int arch_get_memory_phys_device(unsigned long start_pfn);
>>   struct memory_notify {
>>       unsigned long start_pfn;
>>       unsigned long nr_pages;
>> +    int status_change_nid_normal;
>>       int status_change_nid;
>>   };
>>   diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 6a5b90d..b62d429b 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -460,6 +460,34 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>>       return 0;
>>   }
>>   +static void check_nodemasks_changes_online(unsigned long nr_pages,
>> +    struct zone *zone, struct memory_notify *arg)
>> +{
>> +    int nid = zone_to_nid(zone);
>> +    enum zone_type zone_last = ZONE_NORMAL;
>> +
>> +    if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
>> +        zone_last = ZONE_MOVABLE;
>> +
>> +    if (zone_idx(zone) <= zone_last && !node_state(nid, N_NORMAL_MEMORY))
>> +        arg->status_change_nid_normal = nid;
>> +    else
>> +        arg->status_change_nid_normal = -1;
>> +
>> +    if (!node_state(nid, N_HIGH_MEMORY))
>> +        arg->status_change_nid = nid;
>> +    else
>> +        arg->status_change_nid = -1;
>> +}
>> +
>> +static void set_nodemasks(int node, struct memory_notify *arg)
>> +{
>> +    if (arg->status_change_nid_normal >= 0)
>> +        node_set_state(node, N_NORMAL_MEMORY);
>> +
>> +    node_set_state(node, N_HIGH_MEMORY);
>> +}
>> +
>>     int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>>   {
>> @@ -471,13 +499,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>>       struct memory_notify arg;
>>         lock_memory_hotplug();
>> +    /*
>> +     * This doesn't need a lock to do pfn_to_page().
>> +     * The section can't be removed here because of the
>> +     * memory_block->state_mutex.
>> +     */
>> +    zone = page_zone(pfn_to_page(pfn));
>> +
>>       arg.start_pfn = pfn;
>>       arg.nr_pages = nr_pages;
>> -    arg.status_change_nid = -1;
>> +    check_nodemasks_changes_online(nr_pages, zone, &arg);
>>         nid = page_to_nid(pfn_to_page(pfn));
>> -    if (node_present_pages(nid) == 0)
>> -        arg.status_change_nid = nid;
>>         ret = memory_notify(MEM_GOING_ONLINE, &arg);
>>       ret = notifier_to_errno(ret);
>> @@ -487,12 +520,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>>           return ret;
>>       }
>>       /*
>> -     * This doesn't need a lock to do pfn_to_page().
>> -     * The section can't be removed here because of the
>> -     * memory_block->state_mutex.
>> -     */
>> -    zone = page_zone(pfn_to_page(pfn));
>> -    /*
>>        * 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.
>> @@ -517,7 +544,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>>       zone->present_pages += onlined_pages;
>>       zone->zone_pgdat->node_present_pages += onlined_pages;
>>       if (onlined_pages) {
>> -        node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
>> +        set_nodemasks(zone_to_nid(zone), &arg);
>>           if (need_zonelists_rebuild)
>>               build_all_zonelists(NULL, zone);
>>           else
>> @@ -870,6 +897,44 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
>>       return offlined;
>>   }
>>   +static void check_nodemasks_changes_offline(unsigned long nr_pages,
>> +        struct zone *zone, struct memory_notify *arg)
>> +{
>> +    struct pglist_data *pgdat = zone->zone_pgdat;
>> +    unsigned long present_pages = 0;
>> +    enum zone_type zt, zone_last = ZONE_NORMAL;
>> +
>> +    if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
>> +        zone_last = ZONE_MOVABLE;
>> +
>> +    for (zt = 0; zt <= zone_last; zt++)
>> +        present_pages += pgdat->node_zones[zt].present_pages;
>> +    if (zone_idx(zone) <= zone_last && nr_pages >= present_pages)
>> +        arg->status_change_nid_normal = zone_to_nid(zone);
>> +    else
>> +        arg->status_change_nid_normal = -1;
>> +
>> +    zone_last = ZONE_MOVABLE;
>> +    for (; zt <= zone_last; zt++)
>> +        present_pages += pgdat->node_zones[zt].present_pages;
>> +    if (nr_pages >= present_pages)
>> +        arg->status_change_nid = zone_to_nid(zone);
>> +    else
>> +        arg->status_change_nid = -1;
>> +}
>> +
>> +static void clear_nodemasks(int node, struct memory_notify *arg)
>> +{
>> +    if (arg->status_change_nid_normal >= 0)
>> +        node_clear_state(node, N_NORMAL_MEMORY);
>> +
>> +    if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
>> +        return;
>> +
>> +    if (arg->status_change_nid >= 0)
>> +        node_clear_state(node, N_HIGH_MEMORY);
>> +}
>> +
>>   static int __ref offline_pages(unsigned long start_pfn,
>>             unsigned long end_pfn, unsigned long timeout)
>>   {
>> @@ -903,9 +968,7 @@ static int __ref offline_pages(unsigned long start_pfn,
>>         arg.start_pfn = start_pfn;
>>       arg.nr_pages = nr_pages;
>> -    arg.status_change_nid = -1;
>> -    if (nr_pages >= node_present_pages(node))
>> -        arg.status_change_nid = node;
>> +    check_nodemasks_changes_offline(nr_pages, zone, &arg);
>>         ret = memory_notify(MEM_GOING_OFFLINE, &arg);
>>       ret = notifier_to_errno(ret);
>> @@ -973,10 +1036,9 @@ repeat:
>>       if (!populated_zone(zone))
>>           zone_pcp_reset(zone);
>>   -    if (!node_present_pages(node)) {
>> -        node_clear_state(node, N_HIGH_MEMORY);
>> +    clear_nodemasks(node, &arg);
>> +    if (arg.status_change_nid >= 0)
>>           kswapd_stop(node);
>> -    }
>>         vm_total_pages = nr_free_pagecache_pages();
>>       writeback_set_ratelimit();
> 
> 

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