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From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
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: Wed, 29 Apr 2020 07:11:45 +0530
Message-ID: <20200429014145.GD19958@linux.vnet.ibm.com> (raw)
In-Reply-To: <20200428165912.ca1eadefbac56d740e6e8fd1@linux-foundation.org>

> > 
> > 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?

Till the nodes are detected, marking Node 0 as online tends to be redundant.
Because the system doesn't know if its a NUMA or a non-NUMA system.
Once we detect the nodes, we online them immediately. Hence I don't see any
side-effects or negative implications of this change.

However if I am missing anything, please do let me know.

From my part, I have tested this on
1. Non-NUMA Single node but CPUs and memory coming from zero node.
2. Non-NUMA Single node but CPUs and memory coming from non-zero node.
3. NUMA Multi node but with CPUs and memory from node 0.
4. NUMA Multi node but with no CPUs and memory from node 0.

-- 
Thanks and Regards
Srikar Dronamraju

  reply index

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
2020-04-29  1:41     ` Srikar Dronamraju [this message]
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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