linux-kernel - [PATCH v3 0/3] Offline memoryless cpuless node 0

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Date:   Fri,  1 May 2020 08:41:25 +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 0/3] Offline memoryless cpuless node 0

Changelog v2:->v3:
- Resolved comments from Gautham.
Link v2: https://lore.kernel.org/linuxppc-dev/20200428093836.27190-1-srikar@linux.vnet.ibm.com/t/#u

Changelog v1:->v2:
- Rebased to v5.7-rc3
- Updated the changelog.
Link v1: https://lore.kernel.org/linuxppc-dev/20200311110237.5731-1-srikar@linux.vnet.ibm.com/t/#u

Linux kernel configured 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
1. numa_balancing to be enabled on systems with only one online node.
2. Existence of dummy (cpuless and memoryless) node which can confuse
users/scripts looking at output of lscpu / numactl.

This patchset wants to correct this anomaly.

This should only affect systems that have CONFIG_MEMORYLESS_NODES.
Currently there are only 2 architectures ia64 and powerpc that have this
config.

Note: Patch 3 in this patch series depends on patches 1 and 2.
Without patches 1 and 2, patch 3 might crash powerpc.

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 + patches
------------------
 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

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>

Srikar Dronamraju (3):
  powerpc/numa: Set numa_node for all possible cpus
  powerpc/numa: Prefer node id queried from vphn
  mm/page_alloc: Keep memoryless cpuless node 0 offline

 arch/powerpc/mm/numa.c | 35 ++++++++++++++++++++++++-----------
 mm/page_alloc.c        |  4 +++-
 2 files changed, 27 insertions(+), 12 deletions(-)

-- 
2.20.1