From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Mel Gorman <mgorman@suse.de>,
Vlastimil Babka <vbabka@suse.cz>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Christopher Lameter <cl@linux.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline
Date: Thu, 30 Apr 2020 12:48:20 +0530 [thread overview]
Message-ID: <20200430071820.GF19958@linux.vnet.ibm.com> (raw)
In-Reply-To: <20200429122211.GD28637@dhcp22.suse.cz>
* Michal Hocko <mhocko@kernel.org> [2020-04-29 14:22:11]:
> On Wed 29-04-20 07:11:45, Srikar Dronamraju wrote:
> > > >
> > > > 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.
>
> Have you tested on something else than ppc? Each arch does the NUMA
> setup separately and this is a big mess. E.g. x86 marks even memory less
> nodes (see init_memory_less_node) as online.
>
while I have predominantly tested on ppc, I did test on X86 with CONFIG_NUMA
enabled/disabled on both single node and multi node machines.
However, I dont have a cpuless/memoryless x86 system.
> Honestly I have hard time to evaluate the effect of this patch. It makes
> some sense to assume all nodes offline before they get online but this
> is a land mine territory.
>
> I am also not sure what kind of problem this is going to address. You
> have mentioned numa balancing without many details.
1. On a machine with just one node with node number not being 0,
the current setup will end up showing 2 online nodes. And when there are
more than one online nodes, numa_balancing gets enabled.
Without patch
$ grep numa /proc/vmstat
numa_hit 95179
numa_miss 0
numa_foreign 0
numa_interleave 3764
numa_local 95179
numa_other 0
numa_pte_updates 1206973 <----------
numa_huge_pte_updates 4654 <----------
numa_hint_faults 19560 <----------
numa_hint_faults_local 19560 <----------
numa_pages_migrated 0
With patch
$ grep numa /proc/vmstat
numa_hit 322338756
numa_miss 0
numa_foreign 0
numa_interleave 3790
numa_local 322338756
numa_other 0
numa_pte_updates 0 <----------
numa_huge_pte_updates 0 <----------
numa_hint_faults 0 <----------
numa_hint_faults_local 0 <----------
numa_pages_migrated 0
So we have a redundant page hinting numa faults which we can avoid.
2. Few people have complained about existence of this dummy node when
parsing lscpu and numactl o/p. They somehow start to think that the tools
are reporting incorrectly or the kernel is not able to recognize resources
connected to the node.
--
Thanks and Regards
Srikar Dronamraju
next prev parent reply other threads:[~2020-04-30 7:18 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
2020-04-29 1:41 ` Srikar Dronamraju
2020-04-29 12:22 ` Michal Hocko
2020-04-30 7:18 ` Srikar Dronamraju [this message]
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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