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Mon, 19 Dec 2022 16:43:06 +0100 (CET) Message-ID: <20221219154119.550996611@infradead.org> User-Agent: quilt/0.66 Date: Mon, 19 Dec 2022 16:35:36 +0100 From: Peter Zijlstra To: torvalds@linux-foundation.org Cc: corbet@lwn.net, will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com, mark.rutland@arm.com, catalin.marinas@arm.com, dennis@kernel.org, tj@kernel.org, cl@linux.com, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, Herbert Xu , davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, joro@8bytes.org, suravee.suthikulpanit@amd.com, robin.murphy@arm.com, dwmw2@infradead.org, baolu.lu@linux.intel.com, Arnd Bergmann , penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, Andrew Morton , vbabka@suse.cz, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org Subject: [RFC][PATCH 11/12] slub: Replace cmpxchg_double() References: <20221219153525.632521981@infradead.org> MIME-Version: 1.0 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 946B9140015 X-Rspam-User: X-Stat-Signature: ymww7mmb8fi7gzfsehsd3facmigbn6r4 X-HE-Tag: 1671464623-604336 X-HE-Meta: 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 NHVCiME3 f8RIHDF0e6zzXvgycF+NqRnHTWh8g61V1QX5uTEl2dDvnxOI= 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: Signed-off-by: Peter Zijlstra (Intel) Acked-by: Vlastimil Babka --- include/linux/slub_def.h | 12 ++- mm/slab.h | 41 +++++++++++-- mm/slub.c | 146 ++++++++++++++++++++++++++++------------------- 3 files changed, 135 insertions(+), 64 deletions(-) --- a/include/linux/slub_def.h +++ b/include/linux/slub_def.h @@ -39,15 +39,21 @@ enum stat_item { CPU_PARTIAL_FREE, /* Refill cpu partial on free */ CPU_PARTIAL_NODE, /* Refill cpu partial from node partial */ CPU_PARTIAL_DRAIN, /* Drain cpu partial to node partial */ - NR_SLUB_STAT_ITEMS }; + NR_SLUB_STAT_ITEMS +}; /* * When changing the layout, make sure freelist and tid are still compatible * with this_cpu_cmpxchg_double() alignment requirements. */ struct kmem_cache_cpu { - void **freelist; /* Pointer to next available object */ - unsigned long tid; /* Globally unique transaction id */ + union { + struct { + void **freelist; /* Pointer to next available object */ + unsigned long tid; /* Globally unique transaction id */ + }; + freelist_aba_t freelist_tid; + }; struct slab *slab; /* The slab from which we are allocating */ #ifdef CONFIG_SLUB_CPU_PARTIAL struct slab *partial; /* Partially allocated frozen slabs */ --- a/mm/slab.h +++ b/mm/slab.h @@ -5,6 +5,32 @@ * Internal slab definitions */ +/* + * Freelist pointer and counter to cmpxchg together, avoids the typical ABA + * problems with cmpxchg of just a pointer. + */ +typedef union { + struct { + void *freelist; + unsigned long counter; + }; +#ifdef CONFIG_64BIT + u128 full; +#else + u64 full; +#endif +} freelist_aba_t; + +#ifdef CONFIG_64BIT +# ifdef system_has_cmpxchg128 +# define system_has_freelist_aba() system_has_cmpxchg128() +# endif +#else /* CONFIG_64BIT */ +# ifdef system_has_cmpxchg64 +# define system_has_freelist_aba() system_has_cmpxchg64() +# endif +#endif /* CONFIG_64BIT */ + /* Reuses the bits in struct page */ struct slab { unsigned long __page_flags; @@ -34,14 +60,19 @@ struct slab { }; struct kmem_cache *slab_cache; /* Double-word boundary */ - void *freelist; /* first free object */ union { - unsigned long counters; struct { - unsigned inuse:16; - unsigned objects:15; - unsigned frozen:1; + void *freelist; /* first free object */ + union { + unsigned long counters; + struct { + unsigned inuse:16; + unsigned objects:15; + unsigned frozen:1; + }; + }; }; + freelist_aba_t freelist_counter; }; unsigned int __unused; --- a/mm/slub.c +++ b/mm/slub.c @@ -280,7 +280,13 @@ static inline bool kmem_cache_has_cpu_pa /* Poison object */ #define __OBJECT_POISON ((slab_flags_t __force)0x80000000U) /* Use cmpxchg_double */ + +#if defined(system_has_freelist_aba) && \ + defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) #define __CMPXCHG_DOUBLE ((slab_flags_t __force)0x40000000U) +#else +#define __CMPXCHG_DOUBLE ((slab_flags_t __force)0U) +#endif /* * Tracking user of a slab. @@ -496,6 +502,47 @@ static __always_inline void slab_unlock( __bit_spin_unlock(PG_locked, &page->flags); } +static inline bool +__update_freelist_fast(struct slab *slab, + void *freelist_old, unsigned long counters_old, + void *freelist_new, unsigned long counters_new) +{ + + bool ret = false; + +#ifdef system_has_freelist_aba + freelist_aba_t old = { .freelist = freelist_old, .counter = counters_old }; + freelist_aba_t new = { .freelist = freelist_new, .counter = counters_new }; + +#ifdef CONFIG_64BIT + ret = try_cmpxchg128(&slab->freelist_counter.full, &old.full, new.full); +#else + ret = try_cmpxchg64(&slab->freelist_counter.full, &old.full, new.full); +#endif +#endif /* system_has_freelist_aba */ + + return ret; +} + +static inline bool +__update_freelist_slow(struct slab *slab, + void *freelist_old, unsigned long counters_old, + void *freelist_new, unsigned long counters_new) +{ + bool ret = false; + + slab_lock(slab); + if (slab->freelist == freelist_old && + slab->counters == counters_old) { + slab->freelist = freelist_new; + slab->counters = counters_new; + ret = true; + } + slab_unlock(slab); + + return ret; +} + /* * Interrupts must be disabled (for the fallback code to work right), typically * by an _irqsave() lock variant. On PREEMPT_RT the preempt_disable(), which is @@ -503,33 +550,25 @@ static __always_inline void slab_unlock( * allocation/ free operation in hardirq context. Therefore nothing can * interrupt the operation. */ -static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab, +static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *slab, void *freelist_old, unsigned long counters_old, void *freelist_new, unsigned long counters_new, const char *n) { + bool ret; + if (USE_LOCKLESS_FAST_PATH()) lockdep_assert_irqs_disabled(); -#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ - defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) + if (s->flags & __CMPXCHG_DOUBLE) { - if (cmpxchg_double(&slab->freelist, &slab->counters, - freelist_old, counters_old, - freelist_new, counters_new)) - return true; - } else -#endif - { - slab_lock(slab); - if (slab->freelist == freelist_old && - slab->counters == counters_old) { - slab->freelist = freelist_new; - slab->counters = counters_new; - slab_unlock(slab); - return true; - } - slab_unlock(slab); + ret = __update_freelist_fast(slab, freelist_old, counters_old, + freelist_new, counters_new); + } else { + ret = __update_freelist_slow(slab, freelist_old, counters_old, + freelist_new, counters_new); } + if (likely(ret)) + return true; cpu_relax(); stat(s, CMPXCHG_DOUBLE_FAIL); @@ -541,36 +580,26 @@ static inline bool __cmpxchg_double_slab return false; } -static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab, +static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab, void *freelist_old, unsigned long counters_old, void *freelist_new, unsigned long counters_new, const char *n) { -#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ - defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) + bool ret; + if (s->flags & __CMPXCHG_DOUBLE) { - if (cmpxchg_double(&slab->freelist, &slab->counters, - freelist_old, counters_old, - freelist_new, counters_new)) - return true; - } else -#endif - { + ret = __update_freelist_fast(slab, freelist_old, counters_old, + freelist_new, counters_new); + } else { unsigned long flags; local_irq_save(flags); - slab_lock(slab); - if (slab->freelist == freelist_old && - slab->counters == counters_old) { - slab->freelist = freelist_new; - slab->counters = counters_new; - slab_unlock(slab); - local_irq_restore(flags); - return true; - } - slab_unlock(slab); + ret = __update_freelist_slow(slab, freelist_old, counters_old, + freelist_new, counters_new); local_irq_restore(flags); } + if (likely(ret)) + return true; cpu_relax(); stat(s, CMPXCHG_DOUBLE_FAIL); @@ -2168,7 +2197,7 @@ static inline void *acquire_slab(struct VM_BUG_ON(new.frozen); new.frozen = 1; - if (!__cmpxchg_double_slab(s, slab, + if (!__slab_update_freelist(s, slab, freelist, counters, new.freelist, new.counters, "acquire_slab")) @@ -2500,7 +2529,7 @@ static void deactivate_slab(struct kmem_ } - if (!cmpxchg_double_slab(s, slab, + if (!slab_update_freelist(s, slab, old.freelist, old.counters, new.freelist, new.counters, "unfreezing slab")) { @@ -2561,7 +2590,7 @@ static void __unfreeze_partials(struct k new.frozen = 0; - } while (!__cmpxchg_double_slab(s, slab, + } while (!__slab_update_freelist(s, slab, old.freelist, old.counters, new.freelist, new.counters, "unfreezing slab")); @@ -3022,7 +3051,7 @@ static inline void *get_freelist(struct new.inuse = slab->objects; new.frozen = freelist != NULL; - } while (!__cmpxchg_double_slab(s, slab, + } while (!__slab_update_freelist(s, slab, freelist, counters, NULL, new.counters, "get_freelist")); @@ -3295,6 +3324,18 @@ static __always_inline void maybe_wipe_o 0, sizeof(void *)); } +static inline bool +__update_cpu_freelist_fast(struct kmem_cache *s, + void *freelist_old, void *freelist_new, + unsigned long tid) +{ + freelist_aba_t old = { .freelist = freelist_old, .counter = tid }; + freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) }; + + return this_cpu_cmpxchg(s->cpu_slab->freelist_tid.full, + old.full, new.full) == old.full; +} + /* * Inlined fastpath so that allocation functions (kmalloc, kmem_cache_alloc) * have the fastpath folded into their functions. So no function call @@ -3379,11 +3420,7 @@ static __always_inline void *slab_alloc_ * against code executing on this cpu *not* from access by * other cpus. */ - if (unlikely(!this_cpu_cmpxchg_double( - s->cpu_slab->freelist, s->cpu_slab->tid, - object, tid, - next_object, next_tid(tid)))) { - + if (unlikely(!__update_cpu_freelist_fast(s, object, next_object, tid))) { note_cmpxchg_failure("slab_alloc", s, tid); goto redo; } @@ -3517,7 +3554,7 @@ static void __slab_free(struct kmem_cach } } - } while (!cmpxchg_double_slab(s, slab, + } while (!slab_update_freelist(s, slab, prior, counters, head, new.counters, "__slab_free")); @@ -3621,11 +3658,7 @@ static __always_inline void do_slab_free set_freepointer(s, tail_obj, freelist); - if (unlikely(!this_cpu_cmpxchg_double( - s->cpu_slab->freelist, s->cpu_slab->tid, - freelist, tid, - head, next_tid(tid)))) { - + if (unlikely(!__update_cpu_freelist_fast(s, freelist, head, tid))) { note_cmpxchg_failure("slab_free", s, tid); goto redo; } @@ -4319,11 +4352,12 @@ static int kmem_cache_open(struct kmem_c } } -#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ +#if defined(system_has_freelist_aba) && \ defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) - if (system_has_cmpxchg_double() && (s->flags & SLAB_NO_CMPXCHG) == 0) + if (system_has_freelist_aba() && !(s->flags & SLAB_NO_CMPXCHG)) { /* Enable fast mode */ s->flags |= __CMPXCHG_DOUBLE; + } #endif /*