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Wed, 24 May 2023 10:13:10 +0000 Message-ID: Date: Wed, 24 May 2023 12:13:09 +0200 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v3 08/11] slub: Replace cmpxchg_double() Content-Language: en-US To: Peter Zijlstra , 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 , 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 References: <20230515075659.118447996@infradead.org> <20230515080554.453785148@infradead.org> <20230524093246.GP83892@hirez.programming.kicks-ass.net> From: Vlastimil Babka In-Reply-To: <20230524093246.GP83892@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/24/23 11:32, 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. > > The below delta makes things boot again when system_has_cmpxchg128 is > not defined. Right, that should do. > 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. I noticed some comments in mm/slub.c still mention "cmpxchg_double", dunno how much you want to clean it right now or can be postponed. Also some sysfs stats files for CONFIG_SLUB_STATS (not widely used) which we probably might try renaming without breaking anyone, but it's not guaranteed.