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Fri, 16 Jan 2026 14:40:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 0LyVMuVNamnydgAAD6G6ig (envelope-from ); Fri, 16 Jan 2026 14:40:37 +0000 From: Vlastimil Babka Date: Fri, 16 Jan 2026 15:40:32 +0100 Subject: [PATCH v3 12/21] slab: remove the do_slab_free() fastpath MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260116-sheaves-for-all-v3-12-5595cb000772@suse.cz> References: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> In-Reply-To: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> To: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin Cc: Hao Li , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com, Vlastimil Babka X-Mailer: b4 0.14.3 X-Rspamd-Queue-Id: 3D9A0A0005 X-Rspamd-Server: rspam06 X-Stat-Signature: usfwiu71taosox8rtycwxh671fyx564w X-Rspam-User: X-HE-Tag: 1768574468-52646 X-HE-Meta: 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 JhQWcHTU kWiH2C0gl8evEQfugtvKYo/2LHUScKmHC0adW70orhzOP6Ny7/EJ205jNzvajMz6M+UKcUY/kBPhvZ1TVmLnWOQHz/pcnmmwXamzc6GLc8bfTaGnv3uyjIIBCkXrOw5+SGTZSvWGEuCzSLiw0fzl/Suu46grTS8KWuSQ+OtDmPtyLG1fpwVfc7QvYoJqtSk5e9B3tNFmJFhAA+SKfT3bdBsioWEbp7fwyUV8234gEIE8Ve0S2SwFLgR92QhWxovDO83AKsLjDo4QOteaKOZv24qUNl2czwspxelIhhQJPMXMLTJpcFmTsPOzUdljSW2dQabEN X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: We have removed cpu slab usage from allocation paths. Now remove do_slab_free() which was freeing objects to the cpu slab when the object belonged to it. Instead call __slab_free() directly, which was previously the fallback. This simplifies kfree_nolock() - when freeing to percpu sheaf fails, we can call defer_free() directly. Also remove functions that became unused. Reviewed-by: Suren Baghdasaryan Signed-off-by: Vlastimil Babka --- mm/slub.c | 149 ++++++-------------------------------------------------------- 1 file changed, 13 insertions(+), 136 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 6b1280f7900a..b08e775dc4cb 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3682,29 +3682,6 @@ static inline unsigned int init_tid(int cpu) return cpu; } -static inline void note_cmpxchg_failure(const char *n, - const struct kmem_cache *s, unsigned long tid) -{ -#ifdef SLUB_DEBUG_CMPXCHG - unsigned long actual_tid = __this_cpu_read(s->cpu_slab->tid); - - pr_info("%s %s: cmpxchg redo ", n, s->name); - - if (IS_ENABLED(CONFIG_PREEMPTION) && - tid_to_cpu(tid) != tid_to_cpu(actual_tid)) { - pr_warn("due to cpu change %d -> %d\n", - tid_to_cpu(tid), tid_to_cpu(actual_tid)); - } else if (tid_to_event(tid) != tid_to_event(actual_tid)) { - pr_warn("due to cpu running other code. Event %ld->%ld\n", - tid_to_event(tid), tid_to_event(actual_tid)); - } else { - pr_warn("for unknown reason: actual=%lx was=%lx target=%lx\n", - actual_tid, tid, next_tid(tid)); - } -#endif - stat(s, CMPXCHG_DOUBLE_CPU_FAIL); -} - static void init_kmem_cache_cpus(struct kmem_cache *s) { #ifdef CONFIG_PREEMPT_RT @@ -4243,18 +4220,6 @@ static inline bool pfmemalloc_match(struct slab *slab, gfp_t gfpflags) return true; } -static inline bool -__update_cpu_freelist_fast(struct kmem_cache *s, - void *freelist_old, void *freelist_new, - unsigned long tid) -{ - struct freelist_tid old = { .freelist = freelist_old, .tid = tid }; - struct freelist_tid new = { .freelist = freelist_new, .tid = next_tid(tid) }; - - return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid, - &old.freelist_tid, new.freelist_tid); -} - /* * Get the slab's freelist and do not freeze it. * @@ -6162,99 +6127,6 @@ void defer_free_barrier(void) irq_work_sync(&per_cpu_ptr(&defer_free_objects, cpu)->work); } -/* - * Fastpath with forced inlining to produce a kfree and kmem_cache_free that - * can perform fastpath freeing without additional function calls. - * - * The fastpath is only possible if we are freeing to the current cpu slab - * of this processor. This typically the case if we have just allocated - * the item before. - * - * If fastpath is not possible then fall back to __slab_free where we deal - * with all sorts of special processing. - * - * Bulk free of a freelist with several objects (all pointing to the - * same slab) possible by specifying head and tail ptr, plus objects - * count (cnt). Bulk free indicated by tail pointer being set. - */ -static __always_inline void do_slab_free(struct kmem_cache *s, - struct slab *slab, void *head, void *tail, - int cnt, unsigned long addr) -{ - /* cnt == 0 signals that it's called from kfree_nolock() */ - bool allow_spin = cnt; - struct kmem_cache_cpu *c; - unsigned long tid; - void **freelist; - -redo: - /* - * Determine the currently cpus per cpu slab. - * The cpu may change afterward. However that does not matter since - * data is retrieved via this pointer. If we are on the same cpu - * during the cmpxchg then the free will succeed. - */ - c = raw_cpu_ptr(s->cpu_slab); - tid = READ_ONCE(c->tid); - - /* Same with comment on barrier() in __slab_alloc_node() */ - barrier(); - - if (unlikely(slab != c->slab)) { - if (unlikely(!allow_spin)) { - /* - * __slab_free() can locklessly cmpxchg16 into a slab, - * but then it might need to take spin_lock - * for further processing. - * Avoid the complexity and simply add to a deferred list. - */ - defer_free(s, head); - } else { - __slab_free(s, slab, head, tail, cnt, addr); - } - return; - } - - if (unlikely(!allow_spin)) { - if ((in_nmi() || !USE_LOCKLESS_FAST_PATH()) && - local_lock_is_locked(&s->cpu_slab->lock)) { - defer_free(s, head); - return; - } - cnt = 1; /* restore cnt. kfree_nolock() frees one object at a time */ - } - - if (USE_LOCKLESS_FAST_PATH()) { - freelist = READ_ONCE(c->freelist); - - set_freepointer(s, tail, freelist); - - if (unlikely(!__update_cpu_freelist_fast(s, freelist, head, tid))) { - note_cmpxchg_failure("slab_free", s, tid); - goto redo; - } - } else { - __maybe_unused unsigned long flags = 0; - - /* Update the free list under the local lock */ - local_lock_cpu_slab(s, flags); - c = this_cpu_ptr(s->cpu_slab); - if (unlikely(slab != c->slab)) { - local_unlock_cpu_slab(s, flags); - goto redo; - } - tid = c->tid; - freelist = c->freelist; - - set_freepointer(s, tail, freelist); - c->freelist = head; - c->tid = next_tid(tid); - - local_unlock_cpu_slab(s, flags); - } - stat_add(s, FREE_FASTPATH, cnt); -} - static __fastpath_inline void slab_free(struct kmem_cache *s, struct slab *slab, void *object, unsigned long addr) @@ -6271,7 +6143,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object, return; } - do_slab_free(s, slab, object, object, 1, addr); + __slab_free(s, slab, object, object, 1, addr); } #ifdef CONFIG_MEMCG @@ -6280,7 +6152,7 @@ static noinline void memcg_alloc_abort_single(struct kmem_cache *s, void *object) { if (likely(slab_free_hook(s, object, slab_want_init_on_free(s), false))) - do_slab_free(s, virt_to_slab(object), object, object, 1, _RET_IP_); + __slab_free(s, virt_to_slab(object), object, object, 1, _RET_IP_); } #endif @@ -6295,7 +6167,7 @@ void slab_free_bulk(struct kmem_cache *s, struct slab *slab, void *head, * to remove objects, whose reuse must be delayed. */ if (likely(slab_free_freelist_hook(s, &head, &tail, &cnt))) - do_slab_free(s, slab, head, tail, cnt, addr); + __slab_free(s, slab, head, tail, cnt, addr); } #ifdef CONFIG_SLUB_RCU_DEBUG @@ -6321,14 +6193,14 @@ static void slab_free_after_rcu_debug(struct rcu_head *rcu_head) /* resume freeing */ if (slab_free_hook(s, object, slab_want_init_on_free(s), true)) - do_slab_free(s, slab, object, object, 1, _THIS_IP_); + __slab_free(s, slab, object, object, 1, _THIS_IP_); } #endif /* CONFIG_SLUB_RCU_DEBUG */ #ifdef CONFIG_KASAN_GENERIC void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr) { - do_slab_free(cache, virt_to_slab(x), x, x, 1, addr); + __slab_free(cache, virt_to_slab(x), x, x, 1, addr); } #endif @@ -6528,8 +6400,13 @@ 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); + /* + * __slab_free() can locklessly cmpxchg16 into a slab, but then it might + * need to take spin_lock for further processing. + * Avoid the complexity and simply add to a deferred list. + */ if (!free_to_pcs(s, x, false)) - do_slab_free(s, slab, x, x, 0, _RET_IP_); + defer_free(s, x); } EXPORT_SYMBOL_GPL(kfree_nolock); @@ -6955,7 +6832,7 @@ static void __kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p) if (kfence_free(df.freelist)) continue; - do_slab_free(df.s, df.slab, df.freelist, df.tail, df.cnt, + __slab_free(df.s, df.slab, df.freelist, df.tail, df.cnt, _RET_IP_); } while (likely(size)); } @@ -7041,7 +6918,7 @@ __refill_objects(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int min, cnt++; object = get_freepointer(s, object); } while (object); - do_slab_free(s, slab, head, tail, cnt, _RET_IP_); + __slab_free(s, slab, head, tail, cnt, _RET_IP_); } if (refilled >= max) -- 2.52.0