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

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

(9/27/12 2:47 AM), 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.

What's mean 'stale'? I guess

: Currently memory_hotplug doesn't turn on/off node_states[N_NORMAL_MEMORY] and
: then it will be invalid if the platform has highmem. Luckily, almost memory 
: hotplug aware platform don't have highmem, but are not all.

right?
I supporse this patch only meaningful on ARM platform practically.



> 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.

status_change_nid_normal is very ugly to me. When status_change_nid and 
status_change_nid_normal has positive value, they are always the same.
nid and flags value are more natual to me.



> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
>  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;

This is very strange (or ugly) code. ZONE_MOVABLE don't depend on high mem.


> +
> +	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;

Wrong. The onlined node may only have high mem zone. IOW, think fake numa case etc.


> +
> +	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)

Too ugly. just remove this and use node_set_state() directly.

> +{
> +	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.
> +	 */

Please explain the intention of this comment. We think lock_memory_hotplug() close
a race against memory offline directly.


> +	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)
> +{

This should remove ugly memory_notify argument and should be fold 
check_nodemasks_changes_online().


> +	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;

Wrong. Think, a zone has both normal and highmem zone and when admin 
only remove highmem area. you should check pfn too.


> +
> +	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;

You should use #ifdef. otherwise we face unreachable statement warning.

> +
> +	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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