Re: [PATCH v4 08/22] slab: make percpu sheaves compatible with kmalloc_nolock()/kfree_nolock()

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Vlastimil Babka <vbabka@suse.cz> [260123 01:54]:
> Before we enable percpu sheaves for kmalloc caches, we need to make sure
> kmalloc_nolock() and kfree_nolock() will continue working properly and
> not spin when not allowed to.
> 
> Percpu sheaves themselves use local_trylock() so they are already
> compatible. We just need to be careful with the barn->lock spin_lock.
> Pass a new allow_spin parameter where necessary to use
> spin_trylock_irqsave().
> 
> In kmalloc_nolock_noprof() we can now attempt alloc_from_pcs() safely,
> for now it will always fail until we enable sheaves for kmalloc caches
> next. Similarly in kfree_nolock() we can attempt free_to_pcs().
> 
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
> Reviewed-by: Hao Li <hao.li@linux.dev>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

I'd rather have a helper that _mayspin() or something.  That way, when
we know we need to or don't want to, we avoid extra instructions.  We
can also avoid passing true/false and complicating the interface when
it's not necessary.

The way it is written works as well, though.

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>



> ---
>  mm/slub.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 60 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 41e1bf35707c..4ca6bd944854 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2889,7 +2889,8 @@ static void pcs_destroy(struct kmem_cache *s)
>  	s->cpu_sheaves = NULL;
>  }
>  
> -static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn)
> +static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn,
> +					       bool allow_spin)
>  {
>  	struct slab_sheaf *empty = NULL;
>  	unsigned long flags;
> @@ -2897,7 +2898,10 @@ static struct slab_sheaf *barn_get_empty_sheaf(struct node_barn *barn)
>  	if (!data_race(barn->nr_empty))
>  		return NULL;
>  
> -	spin_lock_irqsave(&barn->lock, flags);
> +	if (likely(allow_spin))
> +		spin_lock_irqsave(&barn->lock, flags);
> +	else if (!spin_trylock_irqsave(&barn->lock, flags))
> +		return NULL;
>  
>  	if (likely(barn->nr_empty)) {
>  		empty = list_first_entry(&barn->sheaves_empty,
> @@ -2974,7 +2978,8 @@ static struct slab_sheaf *barn_get_full_or_empty_sheaf(struct node_barn *barn)
>   * change.
>   */
>  static struct slab_sheaf *
> -barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
> +barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty,
> +			 bool allow_spin)
>  {
>  	struct slab_sheaf *full = NULL;
>  	unsigned long flags;
> @@ -2982,7 +2987,10 @@ barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
>  	if (!data_race(barn->nr_full))
>  		return NULL;
>  
> -	spin_lock_irqsave(&barn->lock, flags);
> +	if (likely(allow_spin))
> +		spin_lock_irqsave(&barn->lock, flags);
> +	else if (!spin_trylock_irqsave(&barn->lock, flags))
> +		return NULL;
>  
>  	if (likely(barn->nr_full)) {
>  		full = list_first_entry(&barn->sheaves_full, struct slab_sheaf,
> @@ -3003,7 +3011,8 @@ barn_replace_empty_sheaf(struct node_barn *barn, struct slab_sheaf *empty)
>   * barn. But if there are too many full sheaves, reject this with -E2BIG.
>   */
>  static struct slab_sheaf *
> -barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full)
> +barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full,
> +			bool allow_spin)
>  {
>  	struct slab_sheaf *empty;
>  	unsigned long flags;
> @@ -3014,7 +3023,10 @@ barn_replace_full_sheaf(struct node_barn *barn, struct slab_sheaf *full)
>  	if (!data_race(barn->nr_empty))
>  		return ERR_PTR(-ENOMEM);
>  
> -	spin_lock_irqsave(&barn->lock, flags);
> +	if (likely(allow_spin))
> +		spin_lock_irqsave(&barn->lock, flags);
> +	else if (!spin_trylock_irqsave(&barn->lock, flags))
> +		return ERR_PTR(-EBUSY);
>  
>  	if (likely(barn->nr_empty)) {
>  		empty = list_first_entry(&barn->sheaves_empty, struct slab_sheaf,
> @@ -5008,7 +5020,8 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
>  		return NULL;
>  	}
>  
> -	full = barn_replace_empty_sheaf(barn, pcs->main);
> +	full = barn_replace_empty_sheaf(barn, pcs->main,
> +					gfpflags_allow_spinning(gfp));
>  
>  	if (full) {
>  		stat(s, BARN_GET);
> @@ -5025,7 +5038,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
>  			empty = pcs->spare;
>  			pcs->spare = NULL;
>  		} else {
> -			empty = barn_get_empty_sheaf(barn);
> +			empty = barn_get_empty_sheaf(barn, true);
>  		}
>  	}
>  
> @@ -5165,7 +5178,8 @@ void *alloc_from_pcs(struct kmem_cache *s, gfp_t gfp, int node)
>  }
>  
>  static __fastpath_inline
> -unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
> +unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, gfp_t gfp, size_t size,
> +				 void **p)
>  {
>  	struct slub_percpu_sheaves *pcs;
>  	struct slab_sheaf *main;
> @@ -5199,7 +5213,8 @@ unsigned int alloc_from_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
>  			return allocated;
>  		}
>  
> -		full = barn_replace_empty_sheaf(barn, pcs->main);
> +		full = barn_replace_empty_sheaf(barn, pcs->main,
> +						gfpflags_allow_spinning(gfp));
>  
>  		if (full) {
>  			stat(s, BARN_GET);
> @@ -5700,7 +5715,7 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
>  	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_NOMEMALLOC | gfp_flags;
>  	struct kmem_cache *s;
>  	bool can_retry = true;
> -	void *ret = ERR_PTR(-EBUSY);
> +	void *ret;
>  
>  	VM_WARN_ON_ONCE(gfp_flags & ~(__GFP_ACCOUNT | __GFP_ZERO |
>  				      __GFP_NO_OBJ_EXT));
> @@ -5731,6 +5746,12 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
>  		 */
>  		return NULL;
>  
> +	ret = alloc_from_pcs(s, alloc_gfp, node);
> +	if (ret)
> +		goto success;
> +
> +	ret = ERR_PTR(-EBUSY);
> +
>  	/*
>  	 * Do not call slab_alloc_node(), since trylock mode isn't
>  	 * compatible with slab_pre_alloc_hook/should_failslab and
> @@ -5767,6 +5788,7 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
>  		ret = NULL;
>  	}
>  
> +success:
>  	maybe_wipe_obj_freeptr(s, ret);
>  	slab_post_alloc_hook(s, NULL, alloc_gfp, 1, &ret,
>  			     slab_want_init_on_alloc(alloc_gfp, s), size);
> @@ -6087,7 +6109,8 @@ static void __pcs_install_empty_sheaf(struct kmem_cache *s,
>   * unlocked.
>   */
>  static struct slub_percpu_sheaves *
> -__pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
> +__pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
> +			bool allow_spin)
>  {
>  	struct slab_sheaf *empty;
>  	struct node_barn *barn;
> @@ -6111,7 +6134,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
>  	put_fail = false;
>  
>  	if (!pcs->spare) {
> -		empty = barn_get_empty_sheaf(barn);
> +		empty = barn_get_empty_sheaf(barn, allow_spin);
>  		if (empty) {
>  			pcs->spare = pcs->main;
>  			pcs->main = empty;
> @@ -6125,7 +6148,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
>  		return pcs;
>  	}
>  
> -	empty = barn_replace_full_sheaf(barn, pcs->main);
> +	empty = barn_replace_full_sheaf(barn, pcs->main, allow_spin);
>  
>  	if (!IS_ERR(empty)) {
>  		stat(s, BARN_PUT);
> @@ -6133,7 +6156,8 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
>  		return pcs;
>  	}
>  
> -	if (PTR_ERR(empty) == -E2BIG) {
> +	/* sheaf_flush_unused() doesn't support !allow_spin */
> +	if (PTR_ERR(empty) == -E2BIG && allow_spin) {
>  		/* Since we got here, spare exists and is full */
>  		struct slab_sheaf *to_flush = pcs->spare;
>  
> @@ -6158,6 +6182,14 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
>  alloc_empty:
>  	local_unlock(&s->cpu_sheaves->lock);
>  
> +	/*
> +	 * alloc_empty_sheaf() doesn't support !allow_spin and it's
> +	 * easier to fall back to freeing directly without sheaves
> +	 * than add the support (and to sheaf_flush_unused() above)
> +	 */
> +	if (!allow_spin)
> +		return NULL;
> +
>  	empty = alloc_empty_sheaf(s, GFP_NOWAIT);
>  	if (empty)
>  		goto got_empty;
> @@ -6200,7 +6232,7 @@ __pcs_replace_full_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs)
>   * The object is expected to have passed slab_free_hook() already.
>   */
>  static __fastpath_inline
> -bool free_to_pcs(struct kmem_cache *s, void *object)
> +bool free_to_pcs(struct kmem_cache *s, void *object, bool allow_spin)
>  {
>  	struct slub_percpu_sheaves *pcs;
>  
> @@ -6211,7 +6243,7 @@ bool free_to_pcs(struct kmem_cache *s, void *object)
>  
>  	if (unlikely(pcs->main->size == s->sheaf_capacity)) {
>  
> -		pcs = __pcs_replace_full_main(s, pcs);
> +		pcs = __pcs_replace_full_main(s, pcs, allow_spin);
>  		if (unlikely(!pcs))
>  			return false;
>  	}
> @@ -6333,7 +6365,7 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)
>  			goto fail;
>  		}
>  
> -		empty = barn_get_empty_sheaf(barn);
> +		empty = barn_get_empty_sheaf(barn, true);
>  
>  		if (empty) {
>  			pcs->rcu_free = empty;
> @@ -6453,7 +6485,7 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
>  		goto no_empty;
>  
>  	if (!pcs->spare) {
> -		empty = barn_get_empty_sheaf(barn);
> +		empty = barn_get_empty_sheaf(barn, true);
>  		if (!empty)
>  			goto no_empty;
>  
> @@ -6467,7 +6499,7 @@ static void free_to_pcs_bulk(struct kmem_cache *s, size_t size, void **p)
>  		goto do_free;
>  	}
>  
> -	empty = barn_replace_full_sheaf(barn, pcs->main);
> +	empty = barn_replace_full_sheaf(barn, pcs->main, true);
>  	if (IS_ERR(empty)) {
>  		stat(s, BARN_PUT_FAIL);
>  		goto no_empty;
> @@ -6719,7 +6751,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>  
>  	if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())
>  	    && likely(!slab_test_pfmemalloc(slab))) {
> -		if (likely(free_to_pcs(s, object)))
> +		if (likely(free_to_pcs(s, object, true)))
>  			return;
>  	}
>  
> @@ -6980,6 +7012,12 @@ void kfree_nolock(const void *object)
>  	 * since kasan quarantine takes locks and not supported from NMI.
>  	 */
>  	kasan_slab_free(s, x, false, false, /* skip quarantine */true);
> +
> +	if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())) {
> +		if (likely(free_to_pcs(s, x, false)))
> +			return;
> +	}
> +
>  	do_slab_free(s, slab, x, x, 0, _RET_IP_);
>  }
>  EXPORT_SYMBOL_GPL(kfree_nolock);
> @@ -7532,7 +7570,7 @@ int kmem_cache_alloc_bulk_noprof(struct kmem_cache *s, gfp_t flags, size_t size,
>  		size--;
>  	}
>  
> -	i = alloc_from_pcs_bulk(s, size, p);
> +	i = alloc_from_pcs_bulk(s, flags, size, p);
>  
>  	if (i < size) {
>  		/*
> 
> -- 
> 2.52.0
> 
>