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

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

[Andrew Morton]

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
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

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

[Andrew Morton]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 4831 bytes --]


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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Libo Chen <libo.chen@oracle.com>
Subject: sched/numa: fix task swap by skipping kernel threads
Date: Fri, 23 May 2025 20:51:01 +0800

Patch series "sched/numa: add statistics of numa balance task migration",
v5.

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.  That is to
say, a kernel thread might be incorrectly chosen as B.  However, kernel
thread and user space thread that does not have mm are not supposed to be
covered by NUMA balancing because NUMA balancing only considers user pages
via VMAs.

According to Peter's suggestion for fixing this issue, we use PF_KTHREAD
to skip the kernel thread.  curr->mm is also checked because it is
possible that user_mode_thread() might create a user thread without an mm.
As per Prateek's analysis, after adding the PF_KTHREAD check, there is no
need to further check the PF_IDLE flag:

: - play_idle_precise() already ensures PF_KTHREAD is set before adding
:   PF_IDLE
: 
: - cpu_startup_entry() is only called from the startup thread which
:   should be marked with PF_KTHREAD (based on my understanding looking at
:   commit cff9b2332ab7 ("kernel/sched: Modify initial boot task idle
:   setup"))

In summary, the check in task_numa_compare() now aligns with
task_tick_numa().

Link: https://lkml.kernel.org/r/cover.1748002400.git.yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/eaacc9c9bd37bac92d43a671867d85b2fdad3b06.1748002400.git.yu.c.chen@intel.com
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Libo Chen <libo.chen@oracle.com>
Suggested-by: Michal Koutný <mkoutny@suse.com>
Tested-by: Ayush Jain <Ayush.jain3@amd.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.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 <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 | PF_KTHREAD)) ||
+		    !cur->mm))
 		cur = NULL;
 
 	/*
_

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

sched-numa-fix-task-swap-by-skipping-kernel-threads.patch

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

[Andrew Morton]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 5022 bytes --]


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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Libo Chen <libo.chen@oracle.com>
Subject: sched/numa: fix task swap by skipping kernel threads
Date: Fri, 23 May 2025 20:51:01 +0800

Patch series "sched/numa: add statistics of numa balance task migration",
v6.

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. 
That is to say, a kernel thread might be incorrectly chosen as B. 
However, kernel thread and user space thread that does not have mm are
not supposed to be covered by NUMA balancing because NUMA balancing
only considers user pages via VMAs.

According to Peter's suggestion for fixing this issue, we use
PF_KTHREAD to skip the kernel thread.  curr->mm is also checked because
it is possible that user_mode_thread() might create a user thread
without an mm.  As per Prateek's analysis, after adding the PF_KTHREAD
check, there is no need to further check the PF_IDLE flag:

: - play_idle_precise() already ensures PF_KTHREAD is set before adding
:   PF_IDLE
: 
: - cpu_startup_entry() is only called from the startup thread which
:   should be marked with PF_KTHREAD (based on my understanding looking at
:   commit cff9b2332ab7 ("kernel/sched: Modify initial boot task idle
:   setup"))

In summary, the check in task_numa_compare() now aligns with
task_tick_numa().

Link: https://lkml.kernel.org/r/cover.1748493462.git.yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/43d68b356b25d124f0d222ebedf3859e86eefb9f.1748493462.git.yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/cover.1748002400.git.yu.c.chen@intel.com
Link: https://lkml.kernel.org/r/eaacc9c9bd37bac92d43a671867d85b2fdad3b06.1748002400.git.yu.c.chen@intel.com
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Libo Chen <libo.chen@oracle.com>
Suggested-by: Michal Koutný <mkoutny@suse.com>
Tested-by: Ayush Jain <Ayush.jain3@amd.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
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 <peterz@infradead.org>
Cc: Roman Gushchin <roman.gushchin@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 | PF_KTHREAD)) ||
+		    !cur->mm))
 		cur = NULL;
 
 	/*
_

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

sched-numa-fix-task-swap-by-skipping-kernel-threads.patch