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From: Andrew Morton <akpm@linux-foundation.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Mel Gorman <mgorman@suse.de>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Christopher Lameter <cl@linux.com>,
	linuxppc-dev@lists.ozlabs.org, Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline
Date: Tue, 28 Apr 2020 16:59:12 -0700	[thread overview]
Message-ID: <20200428165912.ca1eadefbac56d740e6e8fd1@linux-foundation.org> (raw)
In-Reply-To: <20200428093836.27190-4-srikar@linux.vnet.ibm.com>

On Tue, 28 Apr 2020 15:08:36 +0530 Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> Currently Linux kernel with CONFIG_NUMA on a system with multiple
> possible nodes, marks node 0 as online at boot.  However in practice,
> there are systems which have node 0 as memoryless and cpuless.
> 
> This can cause numa_balancing to be enabled on systems with only one node
> with memory and CPUs. The existence of this dummy node which is cpuless and
> memoryless node can confuse users/scripts looking at output of lscpu /
> numactl.
> 
> By marking, N_ONLINE as NODE_MASK_NONE, lets stop assuming that Node 0 is
> always online.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -116,8 +116,10 @@ EXPORT_SYMBOL(latent_entropy);
>   */
>  nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
>  	[N_POSSIBLE] = NODE_MASK_ALL,
> +#ifdef CONFIG_NUMA
> +	[N_ONLINE] = NODE_MASK_NONE,
> +#else
>  	[N_ONLINE] = { { [0] = 1UL } },
> -#ifndef CONFIG_NUMA
>  	[N_NORMAL_MEMORY] = { { [0] = 1UL } },
>  #ifdef CONFIG_HIGHMEM
>  	[N_HIGH_MEMORY] = { { [0] = 1UL } },

So on all other NUMA machines, when does node 0 get marked online?

This change means that for some time during boot, such machines will
now be running with node 0 marked as offline.  What are the
implications of this?  Will something break?

  reply	other threads:[~2020-04-29  0:01 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-28  9:38 [PATCH v2 0/3] Offline memoryless cpuless node 0 Srikar Dronamraju
2020-04-28  9:38 ` [PATCH v2 1/3] powerpc/numa: Set numa_node for all possible cpus Srikar Dronamraju
2020-04-28  9:38 ` [PATCH v2 2/3] powerpc/numa: Prefer node id queried from vphn Srikar Dronamraju
2020-04-29  6:52   ` Gautham R Shenoy
2020-04-30  4:34     ` Srikar Dronamraju
2020-04-28  9:38 ` [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Srikar Dronamraju
2020-04-28 23:59   ` Andrew Morton [this message]
2020-04-29  1:41     ` Srikar Dronamraju
2020-04-29 12:22       ` Michal Hocko
2020-04-30  7:18         ` Srikar Dronamraju
2020-05-04  9:37           ` Michal Hocko
2020-05-08 13:03             ` Srikar Dronamraju
2020-05-08 13:39               ` David Hildenbrand
2020-05-08 13:42                 ` David Hildenbrand
2020-05-11 17:47                   ` Srikar Dronamraju
2020-05-12  7:49                     ` David Hildenbrand
2020-05-12 10:42                       ` Srikar Dronamraju

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