I believe this patch should be dropped. Not only it doesn't really describes an actual problem I believe it is indeed incorrect as explained https://lore.kernel.org/all/ZxoEWBakAv64wfhD@tiehlicka/T/#u On Wed 23-10-24 13:41:25, Andrew Morton wrote: > 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 -- Michal Hocko SUSE Labs
