Re: [PATCH v2 2/4] sched: Remove mm_cid_next_scan as obsolete

On 2024-12-13 04:54, Gabriele Monaco wrote:

The checks for the scan time in task_mm_cid_work are now superfluous since the task runs in a delayed_work and the minimum periodicity is already implied.

This patch removes those checks and the field from the mm_struct.

Additionally, we include a simple check to quickly terminate the function if we have no work to be done (i.e. no mm_cid is allocated). This is helpful for tasks that sleep for a long time, but also for terminated task. We are no longer following the process' state, hence the function continues to run after a process terminates but before its mm is freed.

Can you fold it in patch 1/4 ?

Thanks,

Mathieu

Signed-off-by: Gabriele Monaco gmonaco@redhat.com

include/linux/mm_types.h | 7 ------- kernel/sched/core.c | 19 +++---------------- 2 files changed, 3 insertions(+), 23 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 92acb827fee4..8a76a1c09234 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -829,12 +829,6 @@ struct mm_struct { * runqueue locks. */ struct mm_cid __percpu *pcpu_cid;

• /*
  

•  * @mm_cid_next_scan: Next mm_cid scan (in jiffies).
  

•  *
  

•  * When the next mm_cid scan is due (in jiffies).
  

•  */
  

• unsigned long mm_cid_next_scan;
  

  /**
  • @nr_cpus_allowed: Number of CPUs allowed for mm.

@@ -1228,7 +1222,6 @@ static inline int mm_alloc_cid_noprof(struct mm_struct *mm, struct task_struct * return -ENOMEM; mm_init_cid(mm, p); INIT_DELAYED_WORK(&mm->mm_cid_work, task_mm_cid_work);

• mm->mm_cid_next_scan = jiffies + msecs_to_jiffies(MM_CID_SCAN_DELAY); schedule_delayed_work(&mm->mm_cid_work, msecs_to_jiffies(MM_CID_SCAN_DELAY)); return 0;

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e3b27b73301c..30d78fe14eff 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10520,28 +10520,15 @@ static void sched_mm_cid_remote_clear_weight(struct mm_struct *mm, int cpu, void task_mm_cid_work(struct work_struct *work) {

• unsigned long now = jiffies, old_scan, next_scan; struct cpumask *cidmask; struct delayed_work *delayed_work = container_of(work, struct delayed_work, work); struct mm_struct *mm = container_of(delayed_work, struct mm_struct, mm_cid_work); int weight, cpu;

• old_scan = READ_ONCE(mm->mm_cid_next_scan);
• next_scan = now + msecs_to_jiffies(MM_CID_SCAN_DELAY);
• if (!old_scan) {

• unsigned long res;
  

• res = cmpxchg(&mm->mm_cid_next_scan, old_scan, next_scan);
  

• if (res != old_scan)
  

• 	old_scan = res;
  

• else
  

• 	old_scan = next_scan;
  

• }
• if (time_before(now, old_scan))

• goto out;
  

• if (!try_cmpxchg(&mm->mm_cid_next_scan, &old_scan, next_scan))

• goto out;
  

  cidmask = mm_cidmask(mm);

• /* Nothing to clear for now */
• if (cpumask_empty(cidmask))

• goto out;
  

  /* Clear cids that were not recently used. */ for_each_possible_cpu(cpu) sched_mm_cid_remote_clear_old(mm, cpu);