+ sched-numa-fix-task-swap-by-skipping-kernel-threads.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: sched/numa: fix task swap by skipping kernel threads
has been added to the -mm mm-new branch.  Its filename is
     sched-numa-fix-task-swap-by-skipping-kernel-threads.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/sched-numa-fix-task-swap-by-skipping-kernel-threads.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Libo Chen <libo.chen@oracle.com>
Subject: sched/numa: fix task swap by skipping kernel threads
Date: Wed, 7 May 2025 19:17:15 +0800

Patch series "sched/numa: add statistics of numa balance task migration",
v4.

Introduce task migration and swap statistics in the following places:

/sys/fs/cgroup/{GROUP}/memory.stat
/proc/{PID}/sched
/proc/vmstat

These statistics facilitate a rapid evaluation of the performance and
resource utilization of the target workload.


This patch (of 2):

Task swapping is triggered when there are no idle CPUs in task A's
preferred node.  In this case, the NUMA load balancer chooses a task B on
A's preferred node and swaps B with A.  This helps improve NUMA locality
without introducing load imbalance between nodes.

In the current implementation, B's NUMA node preference is not mandatory,
and it aims not to increase load imbalance.  That is to say, a kernel
thread might be chosen as B.  However, kernel threads are not supposed to
be covered by NUMA balancing because NUMA balancing only considers user
pages via VMAs.

Fix this by not considering kernel threads as swap targets in
task_numa_compare().  This can be extended beyond kernel threads in the
future by checking if a swap candidate has a valid NUMA preference through
checking the candidate's numa_preferred_nid and numa_faults.  For now,
keep the code simple.

Link: https://lkml.kernel.org/r/cover.1746611892.git.yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/a541cdf9b97f523f6b8067271847a986db5ba768.1746611892.git.yu.c.chen@intel.com
Signed-off-by: Libo Chen <libo.chen@oracle.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Suggested-by: Michal Koutny <mkoutny@suse.com>
Tested-by: Ayush Jain <Ayush.jain3@amd.com>
Cc: Aubrey Li <aubrey.li@intel.com>
Cc: "Chen, Tim C" <tim.c.chen@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Cc: Mel Gorman <mgorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/sched/fair.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c~sched-numa-fix-task-swap-by-skipping-kernel-threads
+++ a/kernel/sched/fair.c
@@ -2273,7 +2273,8 @@ static bool task_numa_compare(struct tas
 
 	rcu_read_lock();
 	cur = rcu_dereference(dst_rq->curr);
-	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
+	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur) ||
+		    !cur->mm))
 		cur = NULL;
 
 	/*
_

Patches currently in -mm which might be from libo.chen@oracle.com are

sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems.patch
sched-numa-add-tracepoint-that-tracks-the-skipping-of-numa-balancing-due-to-cpuset-memory-pinning.patch
sched-numa-fix-task-swap-by-skipping-kernel-threads.patch