Messages in this thread | | | Date | Fri, 25 Feb 2011 14:46:54 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: [cpuops cmpxchg double V3 4/5] Lockless (and preemptless) fastpaths for slub |
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On Fri, 25 Feb 2011, Mathieu Desnoyers wrote:
> > Index: linux-2.6/include/linux/slub_def.h > > =================================================================== > > --- linux-2.6.orig/include/linux/slub_def.h 2011-02-25 10:45:49.000000000 -0600 > > +++ linux-2.6/include/linux/slub_def.h 2011-02-25 10:46:19.000000000 -0600 > > @@ -35,7 +35,10 @@ enum stat_item { > > NR_SLUB_STAT_ITEMS }; > > > > struct kmem_cache_cpu { > > - void **freelist; /* Pointer to first free per cpu object */ > > + void **freelist; /* Pointer to next available object */ > > +#ifdef CONFIG_CMPXCHG_LOCAL > > + unsigned long tid; /* Globally unique transaction id */ > > +#endif > > There seem to be no strong guarantee that freelist is double-word aligned here.
The struct kmem_cache_cpu allocation via alloc_percpu() specifies double word alignment. See the remainder of the code quoted by you:
> > +#ifdef CONFIG_CMPXCHG_LOCAL > > + /* > > + * Must align to double word boundary for the double cmpxchg instructions > > + * to work. > > + */ > > + s->cpu_slab = __alloc_percpu(sizeof(struct kmem_cache_cpu), 2 * sizeof(void *)); > > +#else > > + /* Regular alignment is sufficient */ > > s->cpu_slab = alloc_percpu(struct kmem_cache_cpu); > > +#endif > > + > > + if (!s->cpu_slab) > > + return 0; > > > > - return s->cpu_slab != NULL; > > + init_kmem_cache_cpus(s); > > + > > + return 1; > > }
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