From ab2f752ac31c0a9e0a38d3dec1ec5d8c5f65f4da Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 23 Jan 2026 07:52:52 +0100 Subject: [PATCH] slab: remove defer_deactivate_slab() There are no more cpu slabs so we don't need their deferred deactivation. The function is now only used from places where we allocate a new slab but then can't spin on node list_lock to put it on the partial list. Instead of the deferred action we can free it directly via __free_slab(), we just need to tell it to use _nolock() freeing of the underlying pages and take care of the accounting. Since free_frozen_pages_nolock() variant does not yet exist for code outside of the page allocator, create it as a trivial wrapper for __free_frozen_pages(..., FPI_TRYLOCK). Reviewed-by: Harry Yoo Reviewed-by: Hao Li Reviewed-by: Suren Baghdasaryan Acked-by: Alexei Starovoitov Signed-off-by: Vlastimil Babka --- mm/internal.h | 1 + mm/page_alloc.c | 5 +++++ mm/slab.h | 8 +------ mm/slub.c | 58 ++++++++++++++++++------------------------------- 4 files changed, 28 insertions(+), 44 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index e430da900430a..1f44ccb4badf4 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -846,6 +846,7 @@ static inline struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned int ord struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned int order); #define alloc_frozen_pages_nolock(...) \ alloc_hooks(alloc_frozen_pages_nolock_noprof(__VA_ARGS__)) +void free_frozen_pages_nolock(struct page *page, unsigned int order); extern void zone_pcp_reset(struct zone *zone); extern void zone_pcp_disable(struct zone *zone); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c380f063e8b7b..0127e9d661ad9 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2981,6 +2981,11 @@ void free_frozen_pages(struct page *page, unsigned int order) __free_frozen_pages(page, order, FPI_NONE); } +void free_frozen_pages_nolock(struct page *page, unsigned int order) +{ + __free_frozen_pages(page, order, FPI_TRYLOCK); +} + /* * Free a batch of folios */ diff --git a/mm/slab.h b/mm/slab.h index 565279a68fd06..f88568e31268e 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -71,13 +71,7 @@ struct slab { struct kmem_cache *slab_cache; union { struct { - union { - struct list_head slab_list; - struct { /* For deferred deactivate_slab() */ - struct llist_node llnode; - void *flush_freelist; - }; - }; + struct list_head slab_list; /* Double-word boundary */ struct freelist_counters; }; diff --git a/mm/slub.c b/mm/slub.c index 4346ace499bb8..883effab47fd3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3262,7 +3262,7 @@ static struct slab *new_slab(struct kmem_cache *s, gfp_t flags, int node) flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node); } -static void __free_slab(struct kmem_cache *s, struct slab *slab) +static void __free_slab(struct kmem_cache *s, struct slab *slab, bool allow_spin) { struct page *page = slab_page(slab); int order = compound_order(page); @@ -3273,14 +3273,26 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab) __ClearPageSlab(page); mm_account_reclaimed_pages(pages); unaccount_slab(slab, order, s); - free_frozen_pages(page, order); + if (allow_spin) + free_frozen_pages(page, order); + else + free_frozen_pages_nolock(page, order); +} + +static void free_new_slab_nolock(struct kmem_cache *s, struct slab *slab) +{ + /* + * Since it was just allocated, we can skip the actions in + * discard_slab() and free_slab(). + */ + __free_slab(s, slab, false); } static void rcu_free_slab(struct rcu_head *h) { struct slab *slab = container_of(h, struct slab, rcu_head); - __free_slab(slab->slab_cache, slab); + __free_slab(slab->slab_cache, slab, true); } static void free_slab(struct kmem_cache *s, struct slab *slab) @@ -3296,7 +3308,7 @@ static void free_slab(struct kmem_cache *s, struct slab *slab) if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU)) call_rcu(&slab->rcu_head, rcu_free_slab); else - __free_slab(s, slab); + __free_slab(s, slab, true); } static void discard_slab(struct kmem_cache *s, struct slab *slab) @@ -3389,8 +3401,6 @@ static void *alloc_single_from_partial(struct kmem_cache *s, return object; } -static void defer_deactivate_slab(struct slab *slab, void *flush_freelist); - /* * Called only for kmem_cache_debug() caches to allocate from a freshly * allocated slab. Allocate a single object instead of whole freelist @@ -3406,8 +3416,8 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s, struct slab *slab, void *object; if (!allow_spin && !spin_trylock_irqsave(&n->list_lock, flags)) { - /* Unlucky, discard newly allocated slab */ - defer_deactivate_slab(slab, NULL); + /* Unlucky, discard newly allocated slab. */ + free_new_slab_nolock(s, slab); return NULL; } @@ -4279,7 +4289,7 @@ static unsigned int alloc_from_new_slab(struct kmem_cache *s, struct slab *slab, if (!spin_trylock_irqsave(&n->list_lock, flags)) { /* Unlucky, discard newly allocated slab */ - defer_deactivate_slab(slab, NULL); + free_new_slab_nolock(s, slab); return 0; } } @@ -6059,7 +6069,6 @@ flush_remote: struct defer_free { struct llist_head objects; - struct llist_head slabs; struct irq_work work; }; @@ -6067,23 +6076,21 @@ static void free_deferred_objects(struct irq_work *work); static DEFINE_PER_CPU(struct defer_free, defer_free_objects) = { .objects = LLIST_HEAD_INIT(objects), - .slabs = LLIST_HEAD_INIT(slabs), .work = IRQ_WORK_INIT(free_deferred_objects), }; /* * In PREEMPT_RT irq_work runs in per-cpu kthread, so it's safe - * to take sleeping spin_locks from __slab_free() and deactivate_slab(). + * to take sleeping spin_locks from __slab_free(). * In !PREEMPT_RT irq_work will run after local_unlock_irqrestore(). */ static void free_deferred_objects(struct irq_work *work) { struct defer_free *df = container_of(work, struct defer_free, work); struct llist_head *objs = &df->objects; - struct llist_head *slabs = &df->slabs; struct llist_node *llnode, *pos, *t; - if (llist_empty(objs) && llist_empty(slabs)) + if (llist_empty(objs)) return; llnode = llist_del_all(objs); @@ -6107,16 +6114,6 @@ static void free_deferred_objects(struct irq_work *work) __slab_free(s, slab, x, x, 1, _THIS_IP_); } - - llnode = llist_del_all(slabs); - llist_for_each_safe(pos, t, llnode) { - struct slab *slab = container_of(pos, struct slab, llnode); - - if (slab->frozen) - deactivate_slab(slab->slab_cache, slab, slab->flush_freelist); - else - free_slab(slab->slab_cache, slab); - } } static void defer_free(struct kmem_cache *s, void *head) @@ -6132,19 +6129,6 @@ static void defer_free(struct kmem_cache *s, void *head) irq_work_queue(&df->work); } -static void defer_deactivate_slab(struct slab *slab, void *flush_freelist) -{ - struct defer_free *df; - - slab->flush_freelist = flush_freelist; - - guard(preempt)(); - - df = this_cpu_ptr(&defer_free_objects); - if (llist_add(&slab->llnode, &df->slabs)) - irq_work_queue(&df->work); -} - void defer_free_barrier(void) { int cpu; -- 2.47.3