linux-kernel - Re: ppc: RECLAIM

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Date:	Tue, 18 Feb 2014 17:43:38 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
cc:	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org, Anton Blanchard <anton@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ppc: RECLAIM_DISTANCE 10?

On Tue, 18 Feb 2014, Nishanth Aravamudan wrote:

> How about the following?
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5de4337..1a0eced 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1854,7 +1854,8 @@ static void __paginginit init_zone_allows_reclaim(int nid)
>         int i;
>  
>         for_each_online_node(i)
> -               if (node_distance(nid, i) <= RECLAIM_DISTANCE)
> +               if (node_distance(nid, i) <= RECLAIM_DISTANCE ||
> +                                       !NODE_DATA(i)->node_present_pages)
>                         node_set(i, NODE_DATA(nid)->reclaim_nodes);
>                 else
>                         zone_reclaim_mode = 1;

 [ I changed the above from NODE_DATA(nid) -> NODE_DATA(i) as you caught 
   so we're looking at the right code. ]

That can't be right, it would allow reclaiming from a memoryless node.  I 
think what you want is

	for_each_online_node(i) {
		if (!node_present_pages(i))
			continue;
		if (node_distance(nid, i) <= RECLAIM_DISTANCE) {
			node_set(i, NODE_DATA(nid)->reclaim_nodes);
			continue;
		}
		/* Always try to reclaim locally */
		zone_reclaim_mode = 1;
	}

but we really should be able to do for_each_node_state(i, N_MEMORY) here 
and memoryless nodes should already be excluded from that mask.

> @@ -4901,13 +4902,13 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
>  
>         pgdat->node_id = nid;
>         pgdat->node_start_pfn = node_start_pfn;
> -       init_zone_allows_reclaim(nid);
>  #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
>         get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
>  #endif
>         calculate_node_totalpages(pgdat, start_pfn, end_pfn,
>                                   zones_size, zholes_size);
>  
> +       init_zone_allows_reclaim(nid);
>         alloc_node_mem_map(pgdat);
>  #ifdef CONFIG_FLAT_NODE_MEM_MAP
>         printk(KERN_DEBUG "free_area_init_node: node %d, pgdat %08lx, node_mem_map %08lx\n",
> 
> I think it's safe to move init_zone_allows_reclaim, because I don't
> think any allocates are occurring here that could cause us to reclaim
> anyways, right? Moving it allows us to safely reference
> node_present_pages.
> 

Yeah, this is fine.
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