Re: [PATCH] SLUB use cmpxchg_local

Christoph Lameter
2007-08-22T20:19:25Z

On Wed, 22 Aug 2007, Mathieu Desnoyers wrote:

> * Christoph Lameter (clameter@sgi.com) wrote:
> > void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
> > @@ -1577,7 +1590,10 @@ static void __slab_free(struct kmem_cach
> > {
> > void *prior;
> > void **object = (void *)x;
> > + unsigned long flags;
> >
> > + local_irq_save(flags);
> > + put_cpu_no_resched();
>
> Those two lines may skip a preempt_check.

Yes we cannot execute something else here.

> Could we change them to this instead ?
>
> put_cpu();
> local_irq_save(flags);

Then the thread could be preempted and rescheduled on a different cpu
between put_cpu and local_irq_save() which means that we loose the
state information of the kmem_cache_cpu structure.

> Otherwise, it would be good to call
>
> preempt_check_resched();
>
> After each local_irq_restore() in this function.

We could do that but maybe the frequency of these checks would be too
high? When should the resched checks be used?