Re: [PATCH 4/4] slub: apply new queue_percpu_work_on() interface

[Leonardo Bras <leobras.c@gmail.com>]

On Fri, Feb 06, 2026 at 11:34:34AM -0300, Marcelo Tosatti wrote:
> Make use of the new qpw_{un,}lock*() and queue_percpu_work_on()
> interface to improve performance & latency on PREEMPT_RT kernels.
> 
> For functions that may be scheduled in a different cpu, replace
> local_{un,}lock*() by qpw_{un,}lock*(), and replace schedule_work_on() by
> queue_percpu_work_on(). The same happens for flush_work() and
> flush_percpu_work().
> 
> This change requires allocation of qpw_structs instead of a work_structs,
> and changing parameters of a few functions to include the cpu parameter.
> 
> This should bring no relevant performance impact on non-RT kernels:

Same as prev patch

> For functions that may be scheduled in a different cpu, the local_*lock's
> this_cpu_ptr() becomes a per_cpu_ptr(smp_processor_id()).
> 
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> ---
>  mm/slub.c |  218 ++++++++++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 142 insertions(+), 76 deletions(-)
> 
> Index: slab/mm/slub.c
> ===================================================================
> --- slab.orig/mm/slub.c
> +++ slab/mm/slub.c
> @@ -49,6 +49,7 @@
>  #include <linux/irq_work.h>
>  #include <linux/kprobes.h>
>  #include <linux/debugfs.h>
> +#include <linux/qpw.h>
>  #include <trace/events/kmem.h>
>  
>  #include "internal.h"
> @@ -128,7 +129,7 @@
>   *   For debug caches, all allocations are forced to go through a list_lock
>   *   protected region to serialize against concurrent validation.
>   *
> - *   cpu_sheaves->lock (local_trylock)
> + *   cpu_sheaves->lock (qpw_trylock)
>   *
>   *   This lock protects fastpath operations on the percpu sheaves. On !RT it
>   *   only disables preemption and does no atomic operations. As long as the main
> @@ -156,7 +157,7 @@
>   *   Interrupts are disabled as part of list_lock or barn lock operations, or
>   *   around the slab_lock operation, in order to make the slab allocator safe
>   *   to use in the context of an irq.
> - *   Preemption is disabled as part of local_trylock operations.
> + *   Preemption is disabled as part of qpw_trylock operations.
>   *   kmalloc_nolock() and kfree_nolock() are safe in NMI context but see
>   *   their limitations.
>   *
> @@ -417,7 +418,7 @@ struct slab_sheaf {
>  };
>  
>  struct slub_percpu_sheaves {
> -	local_trylock_t lock;
> +	qpw_trylock_t lock;
>  	struct slab_sheaf *main; /* never NULL when unlocked */
>  	struct slab_sheaf *spare; /* empty or full, may be NULL */
>  	struct slab_sheaf *rcu_free; /* for batching kfree_rcu() */
> @@ -479,7 +480,7 @@ static nodemask_t slab_nodes;
>  static struct workqueue_struct *flushwq;
>  
>  struct slub_flush_work {
> -	struct work_struct work;
> +	struct qpw_struct qpw;
>  	struct kmem_cache *s;
>  	bool skip;
>  };
> @@ -2826,7 +2827,7 @@ static void __kmem_cache_free_bulk(struc
>   *
>   * returns true if at least partially flushed
>   */
> -static bool sheaf_flush_main(struct kmem_cache *s)
> +static bool sheaf_flush_main(struct kmem_cache *s, int cpu)
>  {
>  	struct slub_percpu_sheaves *pcs;
>  	unsigned int batch, remaining;
> @@ -2835,10 +2836,10 @@ static bool sheaf_flush_main(struct kmem
>  	bool ret = false;
>  
>  next_batch:
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu))
>  		return ret;
>  
> -	pcs = this_cpu_ptr(s->cpu_sheaves);
> +	pcs = per_cpu_ptr(s->cpu_sheaves, cpu);
>  	sheaf = pcs->main;
>  
>  	batch = min(PCS_BATCH_MAX, sheaf->size);
> @@ -2848,7 +2849,7 @@ next_batch:
>  
>  	remaining = sheaf->size;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
>  
>  	__kmem_cache_free_bulk(s, batch, &objects[0]);
>  
> @@ -2932,13 +2933,13 @@ static void rcu_free_sheaf_nobarn(struct
>   * flushing operations are rare so let's keep it simple and flush to slabs
>   * directly, skipping the barn
>   */
> -static void pcs_flush_all(struct kmem_cache *s)
> +static void pcs_flush_all(struct kmem_cache *s, int cpu)
>  {
>  	struct slub_percpu_sheaves *pcs;
>  	struct slab_sheaf *spare, *rcu_free;
>  
> -	local_lock(&s->cpu_sheaves->lock);
> -	pcs = this_cpu_ptr(s->cpu_sheaves);
> +	qpw_lock(&s->cpu_sheaves->lock, cpu);
> +	pcs = per_cpu_ptr(s->cpu_sheaves, cpu);
>  
>  	spare = pcs->spare;
>  	pcs->spare = NULL;
> @@ -2946,7 +2947,7 @@ static void pcs_flush_all(struct kmem_ca
>  	rcu_free = pcs->rcu_free;
>  	pcs->rcu_free = NULL;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
>  
>  	if (spare) {
>  		sheaf_flush_unused(s, spare);
> @@ -2956,7 +2957,7 @@ static void pcs_flush_all(struct kmem_ca
>  	if (rcu_free)
>  		call_rcu(&rcu_free->rcu_head, rcu_free_sheaf_nobarn);
>  
> -	sheaf_flush_main(s);
> +	sheaf_flush_main(s, cpu);
>  }
>  
>  static void __pcs_flush_all_cpu(struct kmem_cache *s, unsigned int cpu)
> @@ -3881,13 +3882,13 @@ static void flush_cpu_sheaves(struct wor
>  {
>  	struct kmem_cache *s;
>  	struct slub_flush_work *sfw;
> +	int cpu = qpw_get_cpu(w);
>  
> -	sfw = container_of(w, struct slub_flush_work, work);
> -
> +	sfw = &per_cpu(slub_flush, cpu);
>  	s = sfw->s;
>  
>  	if (cache_has_sheaves(s))
> -		pcs_flush_all(s);
> +		pcs_flush_all(s, cpu);
>  }
>  
>  static void flush_all_cpus_locked(struct kmem_cache *s)
> @@ -3904,17 +3905,17 @@ static void flush_all_cpus_locked(struct
>  			sfw->skip = true;
>  			continue;
>  		}
> -		INIT_WORK(&sfw->work, flush_cpu_sheaves);
> +		INIT_QPW(&sfw->qpw, flush_cpu_sheaves, cpu);
>  		sfw->skip = false;
>  		sfw->s = s;
> -		queue_work_on(cpu, flushwq, &sfw->work);
> +		queue_percpu_work_on(cpu, flushwq, &sfw->qpw);
>  	}
>  
>  	for_each_online_cpu(cpu) {
>  		sfw = &per_cpu(slub_flush, cpu);
>  		if (sfw->skip)
>  			continue;
> -		flush_work(&sfw->work);
> +		flush_percpu_work(&sfw->qpw);
>  	}
>  
>  	mutex_unlock(&flush_lock);
> @@ -3933,17 +3934,18 @@ static void flush_rcu_sheaf(struct work_
>  	struct slab_sheaf *rcu_free;
>  	struct slub_flush_work *sfw;
>  	struct kmem_cache *s;
> +	int cpu = qpw_get_cpu(w);
>  
> -	sfw = container_of(w, struct slub_flush_work, work);
> +	sfw = &per_cpu(slub_flush, cpu);
>  	s = sfw->s;
>  
> -	local_lock(&s->cpu_sheaves->lock);
> -	pcs = this_cpu_ptr(s->cpu_sheaves);
> +	qpw_lock(&s->cpu_sheaves->lock, cpu);
> +	pcs = per_cpu_ptr(s->cpu_sheaves, cpu);
>  
>  	rcu_free = pcs->rcu_free;
>  	pcs->rcu_free = NULL;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
>  
>  	if (rcu_free)
>  		call_rcu(&rcu_free->rcu_head, rcu_free_sheaf_nobarn);
> @@ -3968,14 +3970,14 @@ void flush_rcu_sheaves_on_cache(struct k
>  		 * sure the __kfree_rcu_sheaf() finished its call_rcu()
>  		 */
>  
> -		INIT_WORK(&sfw->work, flush_rcu_sheaf);
> +		INIT_QPW(&sfw->qpw, flush_rcu_sheaf, cpu);
>  		sfw->s = s;
> -		queue_work_on(cpu, flushwq, &sfw->work);
> +		queue_percpu_work_on(cpu, flushwq, &sfw->qpw);
>  	}
>  
>  	for_each_online_cpu(cpu) {
>  		sfw = &per_cpu(slub_flush, cpu);
> -		flush_work(&sfw->work);
> +		flush_percpu_work(&sfw->qpw);
>  	}
>  
>  	mutex_unlock(&flush_lock);
> @@ -4472,22 +4474,24 @@ bool slab_post_alloc_hook(struct kmem_ca
>   *
>   * Must be called with the cpu_sheaves local lock locked. If successful, returns
>   * the pcs pointer and the local lock locked (possibly on a different cpu than
> - * initially called). If not successful, returns NULL and the local lock
> - * unlocked.
> + * initially called), and migration disabled. If not successful, returns NULL
> + * and the local lock unlocked, with migration enabled.
>   */
>  static struct slub_percpu_sheaves *
> -__pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, gfp_t gfp)
> +__pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, gfp_t gfp,
> +			 int *cpu)
>  {
>  	struct slab_sheaf *empty = NULL;
>  	struct slab_sheaf *full;
>  	struct node_barn *barn;
>  	bool can_alloc;
>  
> -	lockdep_assert_held(this_cpu_ptr(&s->cpu_sheaves->lock));
> +	qpw_lockdep_assert_held(&s->cpu_sheaves->lock);
>  
>  	/* Bootstrap or debug cache, back off */
>  	if (unlikely(!cache_has_sheaves(s))) {
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +		migrate_enable();
>  		return NULL;
>  	}
>  
> @@ -4498,7 +4502,8 @@ __pcs_replace_empty_main(struct kmem_cac
>  
>  	barn = get_barn(s);
>  	if (!barn) {
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +		migrate_enable();
>  		return NULL;
>  	}
>  
> @@ -4524,7 +4529,8 @@ __pcs_replace_empty_main(struct kmem_cac
>  		}
>  	}
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +	migrate_enable();
>  
>  	if (!can_alloc)
>  		return NULL;
> @@ -4550,7 +4556,9 @@ __pcs_replace_empty_main(struct kmem_cac
>  	 * we can reach here only when gfpflags_allow_blocking
>  	 * so this must not be an irq
>  	 */
> -	local_lock(&s->cpu_sheaves->lock);
> +	migrate_disable();
> +	*cpu = smp_processor_id();
> +	qpw_lock(&s->cpu_sheaves->lock, *cpu);
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
>  	/*
> @@ -4593,6 +4601,7 @@ void *alloc_from_pcs(struct kmem_cache *
>  	struct slub_percpu_sheaves *pcs;
>  	bool node_requested;
>  	void *object;
> +	int cpu;
>  
>  #ifdef CONFIG_NUMA
>  	if (static_branch_unlikely(&strict_numa) &&
> @@ -4627,13 +4636,17 @@ void *alloc_from_pcs(struct kmem_cache *
>  		return NULL;
>  	}
>  
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu)) {
> +		migrate_enable();
>  		return NULL;
> +	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
>  	if (unlikely(pcs->main->size == 0)) {
> -		pcs = __pcs_replace_empty_main(s, pcs, gfp);
> +		pcs = __pcs_replace_empty_main(s, pcs, gfp, &cpu);
>  		if (unlikely(!pcs))
>  			return NULL;
>  	}
> @@ -4647,7 +4660,8 @@ void *alloc_from_pcs(struct kmem_cache *
>  		 * the current allocation or previous freeing process.
>  		 */
>  		if (page_to_nid(virt_to_page(object)) != node) {
> -			local_unlock(&s->cpu_sheaves->lock);
> +			qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +			migrate_enable();
>  			stat(s, ALLOC_NODE_MISMATCH);
>  			return NULL;
>  		}
> @@ -4655,7 +4669,8 @@ void *alloc_from_pcs(struct kmem_cache *
>  
>  	pcs->main->size--;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	stat(s, ALLOC_FASTPATH);
>  
> @@ -4670,10 +4685,15 @@ unsigned int alloc_from_pcs_bulk(struct
>  	struct slab_sheaf *main;
>  	unsigned int allocated = 0;
>  	unsigned int batch;
> +	int cpu;
>  
>  next_batch:
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu)) {
> +		migrate_enable();
>  		return allocated;
> +	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
> @@ -4683,7 +4703,8 @@ next_batch:
>  		struct node_barn *barn;
>  
>  		if (unlikely(!cache_has_sheaves(s))) {
> -			local_unlock(&s->cpu_sheaves->lock);
> +			qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +			migrate_enable();
>  			return allocated;
>  		}
>  
> @@ -4694,7 +4715,8 @@ next_batch:
>  
>  		barn = get_barn(s);
>  		if (!barn) {
> -			local_unlock(&s->cpu_sheaves->lock);
> +			qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +			migrate_enable();
>  			return allocated;
>  		}
>  
> @@ -4709,7 +4731,8 @@ next_batch:
>  
>  		stat(s, BARN_GET_FAIL);
>  
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +		migrate_enable();
>  
>  		/*
>  		 * Once full sheaves in barn are depleted, let the bulk
> @@ -4727,7 +4750,8 @@ do_alloc:
>  	main->size -= batch;
>  	memcpy(p, main->objects + main->size, batch * sizeof(void *));
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	stat_add(s, ALLOC_FASTPATH, batch);
>  
> @@ -4877,6 +4901,7 @@ kmem_cache_prefill_sheaf(struct kmem_cac
>  	struct slub_percpu_sheaves *pcs;
>  	struct slab_sheaf *sheaf = NULL;
>  	struct node_barn *barn;
> +	int cpu;
>  
>  	if (unlikely(!size))
>  		return NULL;
> @@ -4906,7 +4931,9 @@ kmem_cache_prefill_sheaf(struct kmem_cac
>  		return sheaf;
>  	}
>  
> -	local_lock(&s->cpu_sheaves->lock);
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	qpw_lock(&s->cpu_sheaves->lock, cpu);
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
>  	if (pcs->spare) {
> @@ -4925,7 +4952,8 @@ kmem_cache_prefill_sheaf(struct kmem_cac
>  			stat(s, BARN_GET_FAIL);
>  	}
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  
>  	if (!sheaf)
> @@ -4961,6 +4989,7 @@ void kmem_cache_return_sheaf(struct kmem
>  {
>  	struct slub_percpu_sheaves *pcs;
>  	struct node_barn *barn;
> +	int cpu;
>  
>  	if (unlikely((sheaf->capacity != s->sheaf_capacity)
>  		     || sheaf->pfmemalloc)) {
> @@ -4969,7 +4998,9 @@ void kmem_cache_return_sheaf(struct kmem
>  		return;
>  	}
>  
> -	local_lock(&s->cpu_sheaves->lock);
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	qpw_lock(&s->cpu_sheaves->lock, cpu);
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  	barn = get_barn(s);
>  
> @@ -4979,7 +5010,8 @@ void kmem_cache_return_sheaf(struct kmem
>  		stat(s, SHEAF_RETURN_FAST);
>  	}
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	if (!sheaf)
>  		return;
> @@ -5507,9 +5539,9 @@ slab_empty:
>   */
>  static void __pcs_install_empty_sheaf(struct kmem_cache *s,
>  		struct slub_percpu_sheaves *pcs, struct slab_sheaf *empty,
> -		struct node_barn *barn)
> +		struct node_barn *barn, int cpu)
>  {
> -	lockdep_assert_held(this_cpu_ptr(&s->cpu_sheaves->lock));
> +	qpw_lockdep_assert_held(&s->cpu_sheaves->lock);
>  
>  	/* This is what we expect to find if nobody interrupted us. */
>  	if (likely(!pcs->spare)) {
> @@ -5546,31 +5578,34 @@ static void __pcs_install_empty_sheaf(st
>  /*
>   * Replace the full main sheaf with a (at least partially) empty sheaf.
>   *
> - * Must be called with the cpu_sheaves local lock locked. If successful, returns
> - * the pcs pointer and the local lock locked (possibly on a different cpu than
> - * initially called). If not successful, returns NULL and the local lock
> - * unlocked.
> + * Must be called with the cpu_sheaves local lock locked, and migration counter

					   ^~ qpw?	

> + * increased. If successful, returns the pcs pointer and the local lock locked
> + * (possibly on a different cpu than initially called), with migration counter
> + * increased. If not successful, returns NULL and the local lock unlocked,

					   		   ^~ qpw?

> + * and migration counter decreased.
>   */
>  static struct slub_percpu_sheaves *
>  __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
> -			bool allow_spin)
> +			bool allow_spin, int *cpu)
>  {
>  	struct slab_sheaf *empty;
>  	struct node_barn *barn;
>  	bool put_fail;
>  
>  restart:
> -	lockdep_assert_held(this_cpu_ptr(&s->cpu_sheaves->lock));
> +	qpw_lockdep_assert_held(&s->cpu_sheaves->lock);
>  
>  	/* Bootstrap or debug cache, back off */
>  	if (unlikely(!cache_has_sheaves(s))) {
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +		migrate_enable();
>  		return NULL;
>  	}
>  
>  	barn = get_barn(s);
>  	if (!barn) {
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +		migrate_enable();
>  		return NULL;
>  	}
>  
> @@ -5607,7 +5642,8 @@ restart:
>  		stat(s, BARN_PUT_FAIL);
>  
>  		pcs->spare = NULL;
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +		migrate_enable();
>  
>  		sheaf_flush_unused(s, to_flush);
>  		empty = to_flush;
> @@ -5623,7 +5659,8 @@ restart:
>  	put_fail = true;
>  
>  alloc_empty:
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, *cpu);
> +	migrate_enable();
>  
>  	/*
>  	 * alloc_empty_sheaf() doesn't support !allow_spin and it's
> @@ -5640,11 +5677,17 @@ alloc_empty:
>  	if (put_fail)
>  		 stat(s, BARN_PUT_FAIL);
>  
> -	if (!sheaf_flush_main(s))
> +	migrate_disable();
> +	*cpu = smp_processor_id();
> +	if (!sheaf_flush_main(s, *cpu)) {
> +		migrate_enable();
>  		return NULL;
> +	}
>  
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, *cpu)) {
> +		migrate_enable();
>  		return NULL;
> +	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
> @@ -5659,13 +5702,14 @@ alloc_empty:
>  	return pcs;
>  
>  got_empty:
> -	if (!local_trylock(&s->cpu_sheaves->lock)) {
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, *cpu)) {
> +		migrate_enable();
>  		barn_put_empty_sheaf(barn, empty);
>  		return NULL;
>  	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
> -	__pcs_install_empty_sheaf(s, pcs, empty, barn);
> +	__pcs_install_empty_sheaf(s, pcs, empty, barn, *cpu);
>  
>  	return pcs;
>  }
> @@ -5678,22 +5722,28 @@ static __fastpath_inline
>  bool free_to_pcs(struct kmem_cache *s, void *object, bool allow_spin)
>  {
>  	struct slub_percpu_sheaves *pcs;
> +	int cpu;
>  
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu)) {
> +		migrate_enable();
>  		return false;
> +	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
>  	if (unlikely(pcs->main->size == s->sheaf_capacity)) {
>  
> -		pcs = __pcs_replace_full_main(s, pcs, allow_spin);
> +		pcs = __pcs_replace_full_main(s, pcs, allow_spin, &cpu);
>  		if (unlikely(!pcs))
>  			return false;
>  	}
>  
>  	pcs->main->objects[pcs->main->size++] = object;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	stat(s, FREE_FASTPATH);
>  
> @@ -5777,14 +5827,19 @@ bool __kfree_rcu_sheaf(struct kmem_cache
>  {
>  	struct slub_percpu_sheaves *pcs;
>  	struct slab_sheaf *rcu_sheaf;
> +	int cpu;
>  
>  	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
>  		return false;
>  
>  	lock_map_acquire_try(&kfree_rcu_sheaf_map);
>  
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu)) {
> +		migrate_enable();
>  		goto fail;
> +	}
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
>  
> @@ -5795,7 +5850,8 @@ bool __kfree_rcu_sheaf(struct kmem_cache
>  
>  		/* Bootstrap or debug cache, fall back */
>  		if (unlikely(!cache_has_sheaves(s))) {
> -			local_unlock(&s->cpu_sheaves->lock);
> +			qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +			migrate_enable();
>  			goto fail;
>  		}
>  
> @@ -5807,7 +5863,8 @@ bool __kfree_rcu_sheaf(struct kmem_cache
>  
>  		barn = get_barn(s);
>  		if (!barn) {
> -			local_unlock(&s->cpu_sheaves->lock);
> +			qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +			migrate_enable();
>  			goto fail;
>  		}
>  
> @@ -5818,15 +5875,18 @@ bool __kfree_rcu_sheaf(struct kmem_cache
>  			goto do_free;
>  		}
>  
> -		local_unlock(&s->cpu_sheaves->lock);
> +		qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +		migrate_enable();
>  
>  		empty = alloc_empty_sheaf(s, GFP_NOWAIT);
>  
>  		if (!empty)
>  			goto fail;
>  
> -		if (!local_trylock(&s->cpu_sheaves->lock)) {
> +		migrate_disable();
> +		if (!qpw_trylock(&s->cpu_sheaves->lock, cpu)) {
>  			barn_put_empty_sheaf(barn, empty);
> +			migrate_enable();
>  			goto fail;
>  		}
>  
> @@ -5862,7 +5922,8 @@ do_free:
>  	if (rcu_sheaf)
>  		call_rcu(&rcu_sheaf->rcu_head, rcu_free_sheaf);
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	stat(s, FREE_RCU_SHEAF);
>  	lock_map_release(&kfree_rcu_sheaf_map);
> @@ -5889,6 +5950,7 @@ static void free_to_pcs_bulk(struct kmem
>  	void *remote_objects[PCS_BATCH_MAX];
>  	unsigned int remote_nr = 0;
>  	int node = numa_mem_id();
> +	int cpu;
>  
>  next_remote_batch:
>  	while (i < size) {
> @@ -5918,7 +5980,9 @@ next_remote_batch:
>  		goto flush_remote;
>  
>  next_batch:
> -	if (!local_trylock(&s->cpu_sheaves->lock))
> +	migrate_disable();
> +	cpu = smp_processor_id();
> +	if (!qpw_trylock(&s->cpu_sheaves->lock, cpu))
>  		goto fallback;
>  
>  	pcs = this_cpu_ptr(s->cpu_sheaves);
> @@ -5961,7 +6025,8 @@ do_free:
>  	memcpy(main->objects + main->size, p, batch * sizeof(void *));
>  	main->size += batch;
>  
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	stat_add(s, FREE_FASTPATH, batch);
>  
> @@ -5977,7 +6042,8 @@ do_free:
>  	return;
>  
>  no_empty:
> -	local_unlock(&s->cpu_sheaves->lock);
> +	qpw_unlock(&s->cpu_sheaves->lock, cpu);
> +	migrate_enable();
>  
>  	/*
>  	 * if we depleted all empty sheaves in the barn or there are too
> @@ -7377,7 +7443,7 @@ static int init_percpu_sheaves(struct km
>  
>  		pcs = per_cpu_ptr(s->cpu_sheaves, cpu);
>  
> -		local_trylock_init(&pcs->lock);
> +		qpw_trylock_init(&pcs->lock);
>  
>  		/*
>  		 * Bootstrap sheaf has zero size so fast-path allocation fails.
> 
> 


Conversions look correct.

I have some ideas, but I am still not sure about the need of 
migrate_*able() here, but if they are indeed needed, I think we should work 
on having them inside helpers that are special for local_cpu-only 
functions, instead of happening on user code like this.

What do you think?

Thanks for getting this upstream!
Leo