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Wed, 24 May 2023 11:32:47 +0200 (CEST) Date: Wed, 24 May 2023 11:32:46 +0200 From: Peter Zijlstra To: torvalds@linux-foundation.org Cc: corbet@lwn.net, will@kernel.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, 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 , Herbert Xu , davem@davemloft.net, 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, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-crypto@vger.kernel.org, sfr@canb.auug.org.au, mpe@ellerman.id.au Subject: Re: [PATCH v3 08/11] slub: Replace cmpxchg_double() Message-ID: <20230524093246.GP83892@hirez.programming.kicks-ass.net> References: <20230515075659.118447996@infradead.org> <20230515080554.453785148@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230515080554.453785148@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Mon, May 15, 2023 at 09:57:07AM +0200, Peter Zijlstra wrote: > @@ -3008,6 +3029,22 @@ static inline bool pfmemalloc_match(stru > } > > #ifndef CONFIG_SLUB_TINY > +static inline bool > +__update_cpu_freelist_fast(struct kmem_cache *s, > + void *freelist_old, void *freelist_new, > + unsigned long tid) > +{ > +#ifdef system_has_freelist_aba > + freelist_aba_t old = { .freelist = freelist_old, .counter = tid }; > + freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) }; > + > + return this_cpu_cmpxchg_freelist(s->cpu_slab->freelist_tid.full, > + old.full, new.full) == old.full; > +#else > + return false; > +#endif > +} > + > /* > * Check the slab->freelist and either transfer the freelist to the > * per cpu freelist or deactivate the slab. > @@ -3359,11 +3396,7 @@ static __always_inline void *__slab_allo > * 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; > } > @@ -3736,11 +3769,7 @@ 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; > } This isn't right; the this_cpu_cmpxchg_double() was unconditional and relied on the local_irq_save() fallback when no native cmpxchg128 is present. The below delta makes things boot again when system_has_cmpxchg128 is not defined. I'm going to zap these patches from tip/locking/core for a few days and fold the below back into the series and let it run through the robots again. --- mm/slab.h | 20 +++++++++++--------- mm/slub.c | 6 +----- 2 files changed, 12 insertions(+), 14 deletions(-) diff --git a/mm/slab.h b/mm/slab.h index 5880c70de3d6..b191bf68e6e0 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -6,36 +6,36 @@ */ void __init kmem_cache_init(void); -#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE #ifdef CONFIG_64BIT # ifdef system_has_cmpxchg128 # define system_has_freelist_aba() system_has_cmpxchg128() # define try_cmpxchg_freelist try_cmpxchg128 -# define this_cpu_cmpxchg_freelist this_cpu_cmpxchg128 -typedef u128 freelist_full_t; # endif +#define this_cpu_cmpxchg_freelist this_cpu_cmpxchg128 +typedef u128 freelist_full_t; #else /* CONFIG_64BIT */ # ifdef system_has_cmpxchg64 # define system_has_freelist_aba() system_has_cmpxchg64() # define try_cmpxchg_freelist try_cmpxchg64 -# define this_cpu_cmpxchg_freelist this_cpu_cmpxchg64 -typedef u64 freelist_full_t; # endif +#define this_cpu_cmpxchg_freelist this_cpu_cmpxchg64 +typedef u64 freelist_full_t; #endif /* CONFIG_64BIT */ -#endif /* CONFIG_HAVE_ALIGNED_STRUCT_PAGE */ + +#if defined(system_has_freelist_aba) && !defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) +#undef system_has_freelist_aba +#endif /* * Freelist pointer and counter to cmpxchg together, avoids the typical ABA * problems with cmpxchg of just a pointer. */ typedef union { -#ifdef system_has_freelist_aba struct { void *freelist; unsigned long counter; }; freelist_full_t full; -#endif } freelist_aba_t; /* Reuses the bits in struct page */ @@ -82,7 +82,9 @@ struct slab { }; }; }; +#ifdef system_has_freelist_aba freelist_aba_t freelist_counter; +#endif }; }; struct rcu_head rcu_head; @@ -110,7 +112,7 @@ SLAB_MATCH(memcg_data, memcg_data); #undef SLAB_MATCH static_assert(sizeof(struct slab) <= sizeof(struct page)); #if defined(system_has_freelist_aba) && defined(CONFIG_SLUB) -static_assert(IS_ALIGNED(offsetof(struct slab, freelist), 2*sizeof(void *))); +static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t))); #endif /** diff --git a/mm/slub.c b/mm/slub.c index 161b091746b7..af92c770606d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3034,15 +3034,11 @@ __update_cpu_freelist_fast(struct kmem_cache *s, void *freelist_old, void *freelist_new, unsigned long tid) { -#ifdef system_has_freelist_aba freelist_aba_t old = { .freelist = freelist_old, .counter = tid }; freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) }; return this_cpu_cmpxchg_freelist(s->cpu_slab->freelist_tid.full, old.full, new.full) == old.full; -#else - return false; -#endif } /*