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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>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.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: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline
Date: Tue, 28 Apr 2020 15:08:36 +0530
Message-ID: <20200428093836.27190-4-srikar@linux.vnet.ibm.com> (raw)
In-Reply-To: <20200428093836.27190-1-srikar@linux.vnet.ibm.com>

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.

v5.7-rc3
 available: 2 nodes (0,2)
 node 0 cpus:
 node 0 size: 0 MB
 node 0 free: 0 MB
 node 2 cpus: 0 1 2 3 4 5 6 7
 node 2 size: 32625 MB
 node 2 free: 31490 MB
 node distances:
 node   0   2
   0:  10  20
   2:  20  10

proc and sys files
------------------
 /sys/devices/system/node/online:            0,2
 /proc/sys/kernel/numa_balancing:            1
 /sys/devices/system/node/has_cpu:           2
 /sys/devices/system/node/has_memory:        2
 /sys/devices/system/node/has_normal_memory: 2
 /sys/devices/system/node/possible:          0-31

v5.7-rc3 + patch
------------------
 available: 1 nodes (2)
 node 2 cpus: 0 1 2 3 4 5 6 7
 node 2 size: 32625 MB
 node 2 free: 31487 MB
 node distances:
 node   2
   2:  10

proc and sys files
------------------
/sys/devices/system/node/online:            2
/proc/sys/kernel/numa_balancing:            0
/sys/devices/system/node/has_cpu:           2
/sys/devices/system/node/has_memory:        2
/sys/devices/system/node/has_normal_memory: 2
/sys/devices/system/node/possible:          0-31

Note: On Powerpc, cpu_to_node of possible but not present cpus would
previously return 0. Hence this commit depends on commit ("powerpc/numa: Set
numa_node for all possible cpus") and commit ("powerpc/numa: Prefer node id
queried from vphn"). Without the 2 commits, Powerpc system might crash.

Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Christopher Lameter <cl@linux.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
Changelog v1:->v2:
- Rebased to v5.7-rc3
- Updated the changelog.

 mm/page_alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 69827d4fa052..03b89592af04 100644
--- 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 } },
-- 
2.20.1


  parent 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 ` Srikar Dronamraju [this message]
2020-04-28 23:59   ` [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Andrew Morton
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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