Changelog v5:->v6: - Now the fix is Powerpc specific. (David Hildenbrand, Michal Hocko, Christopher Lamater) - rebased to v5.8 link v5: https://lore.kernel.org/linuxppc-dev/20200624092846.9194-1-srikar@xxxxxxxxxxxxxxxxxx/t/#u Changelog v4:->v5: - rebased to v5.8 link v4: http://lore.kernel.org/lkml/20200512132937.19295-1-srikar@xxxxxxxxxxxxxxxxxx/t/#u Changelog v3:->v4: - Resolved comments from Christopher. Link v3: http://lore.kernel.org/lkml/20200501031128.19584-1-srikar@xxxxxxxxxxxxxxxxxx/t/#u Changelog v2:->v3: - Resolved comments from Gautham. Link v2: https://lore.kernel.org/linuxppc-dev/20200428093836.27190-1-srikar@xxxxxxxxxxxxxxxxxx/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@xxxxxxxxxxxxxxxxxx/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. v5.8 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 v5.8 + 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 1. User space applications like Numactl, lscpu, that parse the sysfs tend to believe there is an extra online node. This tends to confuse users and applications. Other user space applications start believing that system was not able to use all the resources (i.e missing resources) or the system was not setup correctly. 2. Also existence of dummy node also leads to inconsistent information. The number of online nodes is inconsistent with the information in the device-tree and resource-dump 3. When the dummy node is present, single node non-Numa systems end up showing up as NUMA systems and numa_balancing gets enabled. This will mean we take the hit from the unnecessary numa hinting faults. 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 3864714 numa_miss 0 numa_foreign 0 numa_interleave 2872 numa_local 3864714 numa_other 0 numa_pte_updates 13739278 <---------- numa_huge_pte_updates 0 <---------- numa_hint_faults 13717222 <---------- numa_hint_faults_local 13717222 <---------- numa_pages_migrated 0 With patch $ grep numa /proc/vmstat numa_hit 6633324 numa_miss 0 numa_foreign 0 numa_interleave 2864 numa_local 6633324 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 Here are 2 sample numa programs. numa01.sh is a set of 2 process each running threads as many as number of cpus; each thread doing 50 loops on 3GB process shared memory operations. numa02.sh is a single process with threads as many as number of cpus; each thread doing 800 loops on 32MB thread local memory operations. Without patch ------------- Testcase Time: Min Max Avg StdDev ./numa01.sh Real: 164.67 164.89 164.76 0.07 ./numa01.sh Sys: 2.88 3.38 3.05 0.17 ./numa01.sh User: 1297.85 1301.82 1300.86 1.51 ./numa02.sh Real: 27.44 27.46 27.45 0.01 ./numa02.sh Sys: 0.15 0.25 0.21 0.03 ./numa02.sh User: 216.65 216.93 216.80 0.09 With patch ----------- Testcase Time: Min Max Avg StdDev %Change ./numa01.sh Real: 164.20 164.38 164.28 0.08 0.292184% ./numa01.sh Sys: 0.72 0.90 0.82 0.06 271.951% ./numa01.sh User: 1300.39 1301.97 1300.94 0.56 -0.0061494% ./numa02.sh Real: 27.41 27.51 27.45 0.03 0% ./numa02.sh Sys: 0.09 0.16 0.13 0.03 61.5385% ./numa02.sh User: 216.38 216.91 216.64 0.21 0.0738552% numa01.sh param no_patch with_patch %Change ----- ---------- ---------- ------- numa_hint_faults 2946055 0 -100% numa_hint_faults_local 2946055 0 -100% numa_hit 700617 681234 -2.76656% numa_local 700617 681234 -2.76656% numa_pte_updates 2947175 0 -100% pgfault 4125926 1120053 -72.8533% pgmajfault 269 181 -32.7138% numa02.sh param no_patch with_patch %Change ----- ---------- ---------- ------- numa_hint_faults 137623 0 -100% numa_hint_faults_local 137623 0 -100% numa_hit 51332 54645 6.45406% numa_local 51332 54645 6.45406% numa_pte_updates 138903 0 -100% pgfault 247058 116743 -52.7467% pgmajfault 154 157 1.94805% Observations: The real time and user time actually doesn't change much. However the system time changes to some extent. The reason being the number of numa hinting faults. With the patch we are not seeing the numa hinting faults. Cc: linuxppc-dev@xxxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Christopher Lameter <cl@xxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx> Cc: Satheesh Rajendran <sathnaga@xxxxxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> Srikar Dronamraju (3): powerpc/numa: Set numa_node for all possible cpus powerpc/numa: Prefer node id queried from vphn powerpc/numa: Offline memoryless cpuless node 0 arch/powerpc/mm/numa.c | 45 ++++++++++++++++++++++++++++++++---------- 1 file changed, 35 insertions(+), 10 deletions(-) -- 2.18.1
