Re: [RFC PATCH 1/2] mm, memory_hotplug: drop artificial restriction on online/offline

[Vlastimil Babka]

On 05/24/2017 02:24 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> 74d42d8fe146 ("memory_hotplug: ensure every online node has NORMAL
> memory") has added can_offline_normal which checks the amount of
> memory in !movable zones as long as CONFIG_MOVABLE_NODE is disable.
> It disallows to offline memory if there is nothing left with a
> justification that "memory-management acts bad when we have nodes which
> is online but don't have any normal memory".
> 
> 74d42d8fe146 ("memory_hotplug: ensure every online node has NORMAL
> memory")

That's the same commit as above... one of them should be different?

> has introduced a restriction that every numa node has to have
> at least some memory in !movable zones before a first movable memory
> can be onlined if !CONFIG_MOVABLE_NODE with the same justification
> 
> While it is true that not having _any_ memory for kernel allocations on
> a NUMA node is far from great and such a node would be quite subotimal
> because all kernel allocations will have to fallback to another NUMA
> node but there is no reason to disallow such a configuration in
> principle.
> 
> Besides that there is not really a big difference to have one memblock
> for ZONE_NORMAL available or none. With 128MB size memblocks the system
> might trash on the kernel allocations requests anyway. It is really
> hard to draw a line on how much normal memory is really sufficient so
> we have to rely on administrator to configure system sanely therefore
> drop the artificial restriction and remove can_offline_normal and
> can_online_high_movable altogether.
> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

-

> mm, memory_hotplug: drop can_online_high_movable
> 
>  because "memory-management acts
> bad when we have nodes which is online but don't have any normal memory.
> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

-
Some editing issue?

Otherwise makes sense to me.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  mm/memory_hotplug.c | 58 -----------------------------------------------------
>  1 file changed, 58 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 599c675ad538..10052c2fd400 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -763,23 +763,6 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  	return 0;
>  }
>  
> -#ifdef CONFIG_MOVABLE_NODE
> -/*
> - * When CONFIG_MOVABLE_NODE, we permit onlining of a node which doesn't have
> - * normal memory.
> - */
> -static bool can_online_high_movable(int nid)
> -{
> -	return true;
> -}
> -#else /* CONFIG_MOVABLE_NODE */
> -/* ensure every online node has NORMAL memory */
> -static bool can_online_high_movable(int nid)
> -{
> -	return node_state(nid, N_NORMAL_MEMORY);
> -}
> -#endif /* CONFIG_MOVABLE_NODE */
> -
>  /* check which state of node_states will be changed when online memory */
>  static void node_states_check_changes_online(unsigned long nr_pages,
>  	struct zone *zone, struct memory_notify *arg)
> @@ -979,9 +962,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  	if (!allow_online_pfn_range(nid, pfn, nr_pages, online_type))
>  		return -EINVAL;
>  
> -	if (online_type == MMOP_ONLINE_MOVABLE && !can_online_high_movable(nid))
> -		return -EINVAL;
> -
>  	/* associate pfn range with the zone */
>  	zone = move_pfn_range(online_type, nid, pfn, nr_pages);
>  
> @@ -1579,41 +1559,6 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
>  	return offlined;
>  }
>  
> -#ifdef CONFIG_MOVABLE_NODE
> -/*
> - * When CONFIG_MOVABLE_NODE, we permit offlining of a node which doesn't have
> - * normal memory.
> - */
> -static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
> -{
> -	return true;
> -}
> -#else /* CONFIG_MOVABLE_NODE */
> -/* ensure the node has NORMAL memory if it is still online */
> -static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
> -{
> -	struct pglist_data *pgdat = zone->zone_pgdat;
> -	unsigned long present_pages = 0;
> -	enum zone_type zt;
> -
> -	for (zt = 0; zt <= ZONE_NORMAL; zt++)
> -		present_pages += pgdat->node_zones[zt].present_pages;
> -
> -	if (present_pages > nr_pages)
> -		return true;
> -
> -	present_pages = 0;
> -	for (; zt <= ZONE_MOVABLE; zt++)
> -		present_pages += pgdat->node_zones[zt].present_pages;
> -
> -	/*
> -	 * we can't offline the last normal memory until all
> -	 * higher memory is offlined.
> -	 */
> -	return present_pages == 0;
> -}
> -#endif /* CONFIG_MOVABLE_NODE */
> -
>  static int __init cmdline_parse_movable_node(char *p)
>  {
>  #ifdef CONFIG_MOVABLE_NODE
> @@ -1741,9 +1686,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  	node = zone_to_nid(zone);
>  	nr_pages = end_pfn - start_pfn;
>  
> -	if (zone_idx(zone) <= ZONE_NORMAL && !can_offline_normal(zone, nr_pages))
> -		return -EINVAL;
> -
>  	/* set above range as isolated */
>  	ret = start_isolate_page_range(start_pfn, end_pfn,
>  				       MIGRATE_MOVABLE, true);
>