linux-kernel - Re: [PATCH v4 3/5] powerpc/mm: allow memory hotplug into a memoryless node

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Date:   Thu, 20 Oct 2016 14:30:42 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Alistair Popple <apopple@....ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Tang Chen <tangchen@...fujitsu.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        devicetree@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 3/5] powerpc/mm: allow memory hotplug into a memoryless
 node



On 07/10/16 05:36, Reza Arbab wrote:
> Remove the check which prevents us from hotplugging into an empty node.
> 
> This limitation has been questioned before [1], and judging by the
> response, there doesn't seem to be a reason we can't remove it. No issues
> have been found in light testing.
> 
> [1] http://lkml.kernel.org/r/CAGZKiBrmkSa1yyhbf5hwGxubcjsE5SmkSMY4tpANERMe2UG4bg@mail.gmail.com
>     http://lkml.kernel.org/r/20160511215051.GF22115@arbab-laptop.austin.ibm.com
> 
> Signed-off-by: Reza Arbab <arbab@...ux.vnet.ibm.com>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Acked-by: Balbir Singh <bsingharora@...il.com>
> Cc: Nathan Fontenot <nfont@...ux.vnet.ibm.com>
> Cc: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/mm/numa.c | 13 +------------
>  1 file changed, 1 insertion(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 75b9cd6..d7ac419 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -1121,7 +1121,7 @@ static int hot_add_node_scn_to_nid(unsigned long scn_addr)
>  int hot_add_scn_to_nid(unsigned long scn_addr)
>  {
>  	struct device_node *memory = NULL;
> -	int nid, found = 0;
> +	int nid;
>  
>  	if (!numa_enabled || (min_common_depth < 0))
>  		return first_online_node;
> @@ -1137,17 +1137,6 @@ int hot_add_scn_to_nid(unsigned long scn_addr)
>  	if (nid < 0 || !node_online(nid))
>  		nid = first_online_node;
>  
> -	if (NODE_DATA(nid)->node_spanned_pages)
> -		return nid;
> -
> -	for_each_online_node(nid) {
> -		if (NODE_DATA(nid)->node_spanned_pages) {
> -			found = 1;
> -			break;
> -		}
> -	}
> -
> -	BUG_ON(!found);
>  	return nid;

FYI, these checks were temporary to begin with

I found this in git history

b226e462124522f2f23153daff31c311729dfa2f (powerpc: don't add memory to empty node/zone)

Balbir Singh.