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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> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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?