linux-kernel - Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline

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Date:   Mon, 3 Dec 2018 19:53:52 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Pingfan Liu <kernelfans@...il.com>
cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node
 offline

On Tue, 4 Dec 2018, Pingfan Liu wrote:

> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 76f8db0..8324953 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -453,6 +453,8 @@ static inline int gfp_zonelist(gfp_t flags)
>   */
>  static inline struct zonelist *node_zonelist(int nid, gfp_t flags)
>  {
> +	if (unlikely(!node_online(nid)))
> +		nid = first_online_node;
>  	return NODE_DATA(nid)->node_zonelists + gfp_zonelist(flags);
>  }
>  

So we're passing the node id from dev_to_node() to kmalloc which 
interprets that as the preferred node and then does node_zonelist() to 
find the zonelist at allocation time.

What happens if we fix this in alloc_dr()?  Does anything else cause 
problems?

And rather than using first_online_node, would next_online_node() work?

I'm thinking about this:

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -100,6 +100,8 @@ static __always_inline struct devres * alloc_dr(dr_release_t release,
 					&tot_size)))
 		return NULL;
 
+	if (unlikely(!node_online(nid)))
+		nid = next_online_node(nid);
 	dr = kmalloc_node_track_caller(tot_size, gfp, nid);
 	if (unlikely(!dr))
 		return NULL;