Re: [PATCH 6.12.y] mm/slab/kvfree_rcu: Switch to WQ_MEM_RECLAIM wq

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found matching upstream commit but patch is missing proper reference to it
ℹ️ Patch is missing in 6.13.y (ignore if backport was sent)
⚠️ Commit missing in all newer stable branches

Found matching upstream commit: dfd3df31c9db752234d7d2e09bef2aeabb643ce4

Status in newer kernel trees:
6.13.y | Not found

Note: The patch differs from the upstream commit:
---
1:  dfd3df31c9db7 ! 1:  b4fb63fe8c845 mm/slab/kvfree_rcu: Switch to WQ_MEM_RECLAIM wq
    @@ Commit message
         Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
         Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
     
    - ## mm/slab_common.c ##
    -@@ mm/slab_common.c: module_param(rcu_min_cached_objs, int, 0444);
    - static int rcu_delay_page_cache_fill_msec = 5000;
    - module_param(rcu_delay_page_cache_fill_msec, int, 0444);
    + ## kernel/rcu/tree.c ##
    +@@ kernel/rcu/tree.c: void call_rcu(struct rcu_head *head, rcu_callback_t func)
    + }
    + EXPORT_SYMBOL_GPL(call_rcu);
      
     +static struct workqueue_struct *rcu_reclaim_wq;
     +
      /* Maximum number of jiffies to wait before draining a batch. */
      #define KFREE_DRAIN_JIFFIES (5 * HZ)
      #define KFREE_N_BATCHES 2
    -@@ mm/slab_common.c: __schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
    +@@ kernel/rcu/tree.c: __schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
      	if (delayed_work_pending(&krcp->monitor_work)) {
      		delay_left = krcp->monitor_work.timer.expires - jiffies;
      		if (delay < delay_left)
    @@ mm/slab_common.c: __schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
      }
      
      static void
    -@@ mm/slab_common.c: kvfree_rcu_queue_batch(struct kfree_rcu_cpu *krcp)
    +@@ kernel/rcu/tree.c: kvfree_rcu_queue_batch(struct kfree_rcu_cpu *krcp)
      			// "free channels", the batch can handle. Break
      			// the loop since it is done with this CPU thus
      			// queuing an RCU work is _always_ success here.
    @@ mm/slab_common.c: kvfree_rcu_queue_batch(struct kfree_rcu_cpu *krcp)
      			WARN_ON_ONCE(!queued);
      			break;
      		}
    -@@ mm/slab_common.c: run_page_cache_worker(struct kfree_rcu_cpu *krcp)
    +@@ kernel/rcu/tree.c: run_page_cache_worker(struct kfree_rcu_cpu *krcp)
      	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
      			!atomic_xchg(&krcp->work_in_progress, 1)) {
      		if (atomic_read(&krcp->backoff_page_cache_fill)) {
    @@ mm/slab_common.c: run_page_cache_worker(struct kfree_rcu_cpu *krcp)
      				&krcp->page_cache_work,
      					msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
      		} else {
    -@@ mm/slab_common.c: void __init kvfree_rcu_init(void)
    +@@ kernel/rcu/tree.c: static void __init kfree_rcu_batch_init(void)
      	int i, j;
      	struct shrinker *kfree_rcu_shrinker;
      
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.12.y       |  Success    |  Success   |