The patch titled
Subject: mm/page_alloc: fix NUMA stats update for cpu-less nodes
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-page_alloc-fix-numa-stats-update-for-cpu-less-nodes.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-fix-numa-stats-update-for-cpu-less-nodes.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Dongjoo Seo <dongjoo.linux.dev@xxxxxxxxx>
Subject: mm/page_alloc: fix NUMA stats update for cpu-less nodes
Date: Wed, 23 Oct 2024 10:50:37 -0700
In the case of memoryless node, when a process prefers a node with no
memory(e.g., because it is running on a CPU local to that node), the
kernel treats a nearby node with memory as the preferred node. As a
result, such allocations do not increment the numa_foreign counter on the
memoryless node, leading to skewed NUMA_HIT, NUMA_MISS, and NUMA_FOREIGN
stats for the nearest node.
This patch corrects this issue by:
1. Checking if the zone or preferred zone is CPU-less before updating
the NUMA stats.
2. Ensuring NUMA_HIT is only updated if the zone is not CPU-less.
3. Ensuring NUMA_FOREIGN is only updated if the preferred zone is not
CPU-less.
Example Before and After Patch:
- Before Patch:
node0 node1 node2
numa_hit 86333181 114338269 5108
numa_miss 5199455 0 56844591
numa_foreign 32281033 29763013 0
interleave_hit 91 91 0
local_node 86326417 114288458 0
other_node 5206219 49768 56849702
- After Patch:
node0 node1 node2
numa_hit 2523058 9225528 0
numa_miss 150213 10226 21495942
numa_foreign 17144215 4501270 0
interleave_hit 91 94 0
local_node 2493918 9208226 0
other_node 179351 27528 21495942
Similarly, in the context of cpuless nodes, this patch ensures that NUMA
statistics are accurately updated by adding checks to prevent the
miscounting of memory allocations when the involved nodes have no CPUs.
This ensures more precise tracking of memory access patterns accross all
nodes, regardless of whether they have CPUs or not, improving the overall
reliability of NUMA stat. The reason is that page allocation from
dev_dax, cpuset, memcg .. comes with preferred allocating zone in cpuless
node and its hard to track the zone info for miss information.
Link: https://lkml.kernel.org/r/20241023175037.9125-1-dongjoo.linux.dev@xxxxxxxxx
Signed-off-by: Dongjoo Seo <dongjoo.linux.dev@xxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Fan Ni <nifan@xxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Adam Manzanares <a.manzanares@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-fix-numa-stats-update-for-cpu-less-nodes
+++ a/mm/page_alloc.c
@@ -2858,19 +2858,21 @@ static inline void zone_statistics(struc
{
#ifdef CONFIG_NUMA
enum numa_stat_item local_stat = NUMA_LOCAL;
+ bool z_is_cpuless = !node_state(zone_to_nid(z), N_CPU);
+ bool pref_is_cpuless = !node_state(zone_to_nid(preferred_zone), N_CPU);
- /* skip numa counters update if numa stats is disabled */
if (!static_branch_likely(&vm_numa_stat_key))
return;
- if (zone_to_nid(z) != numa_node_id())
+ if (zone_to_nid(z) != numa_node_id() || z_is_cpuless)
local_stat = NUMA_OTHER;
- if (zone_to_nid(z) == zone_to_nid(preferred_zone))
+ if (zone_to_nid(z) == zone_to_nid(preferred_zone) && !z_is_cpuless)
__count_numa_events(z, NUMA_HIT, nr_account);
else {
__count_numa_events(z, NUMA_MISS, nr_account);
- __count_numa_events(preferred_zone, NUMA_FOREIGN, nr_account);
+ if (!pref_is_cpuless)
+ __count_numa_events(preferred_zone, NUMA_FOREIGN, nr_account);
}
__count_numa_events(z, local_stat, nr_account);
#endif
_
Patches currently in -mm which might be from dongjoo.linux.dev@xxxxxxxxx are
mm-page_alloc-fix-numa-stats-update-for-cpu-less-nodes.patch
