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Date: Fri, 1 May 2020 08:41:28 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Christopher Lameter <cl@...ux.com>,
Michael Ellerman <mpe@...erman.id.au>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Subject: [PATCH v3 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline
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@...ts.ozlabs.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Cc: Michal Hocko <mhocko@...e.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Christopher Lameter <cl@...ux.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
Changelog v1:->v2:
- Rebased to v5.7-rc3
Link v2: https://lore.kernel.org/linuxppc-dev/20200428093836.27190-1-srikar@linux.vnet.ibm.com/t/#u
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
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