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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1q40FD-006M99-Vy; Tue, 30 May 2023 14:22:42 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id E4605300233; Tue, 30 May 2023 16:22:32 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A11CD2414735F; Tue, 30 May 2023 16:22:32 +0200 (CEST) Date: Tue, 30 May 2023 16:22:32 +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, James.Bottomley@hansenpartnership.com, deller@gmx.de, linux-parisc@vger.kernel.org Subject: Re: [PATCH v3 08/11] slub: Replace cmpxchg_double() Message-ID: <20230530142232.GA200270@hirez.programming.kicks-ass.net> References: <20230515075659.118447996@infradead.org> <20230515080554.453785148@infradead.org> <20230524093246.GP83892@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230524093246.GP83892@hirez.programming.kicks-ass.net> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D9E3DA001C X-Stat-Signature: 891qyo11syh3pdsbopaanhufteidk9p4 X-HE-Tag: 1685456611-471380 X-HE-Meta: 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 O9XgtYoY hZmrE+4X+xyccHrRVMppiaW9Vnh9N216/sDRiBeBKtp8ccN1VrrL9mErDl0y8fhDhwr80q1aKiCygKHDA7chyXOuf8PV+lOhp86NPSBlVuQEzhY2k8asuzsNK4M34RI4MNGuFtymhdeUS0bq8hP30eojRhMLTWvmCY48o7ZzK3UrA1Sqd7tOzMkZHVXEvfjatwhDoxLCiIe3jTIT+WQJMTIwFC0T6qDEAqkAMaTmZmQyldp9ymCdAsaOINnVasbfr1n+T 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: On Wed, May 24, 2023 at 11:32:47AM +0200, Peter Zijlstra wrote: > 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. This means this_cpu_cmpxchg128 is expected to be present on all 64bit archs, except Mark just found out that HPPA doens't support __int128 until gcc-11. (I've been building using gcc-12.2) And because the cmpxchg128 fallback relies on '==' we can't trivally fudge that with a struct type either :/ Now, afaict it all magically works if I use: #ifdef __SIZEOF_INT128__ typedef __s128 s128 typedef __u128 u128 #else #if defined(CONFIG_PARISC) && defined(CONFIG_64BIT) typedef long double u128; #endif #endif but that is *super* gross. The alternative is raising the minimum GCC for PARISC to gcc-11.. Yet another alternative is using a struct type and an equality function, just for this. Anybody?