Re: [PATCH] slub: Avoid irqoff/on in bulk allocation

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Wed, 2 Sep 2015 13:04:08 -0500 (CDT)
Christoph Lameter <cl@linux.com> wrote:

> On Wed, 2 Sep 2015, Jesper Dangaard Brouer wrote:
> 
> > > +error:
> > > +	__kmem_cache_free_bulk(s, i, p);
> >
> > Don't we need to update "tid" here, like:
> >
> >   c->tid = next_tid(c->tid);
> >
> > Consider a call to the ordinary kmem_cache_alloc/slab_alloc_node was
> > in-progress, which get PREEMPT'ed just before it's call to
> > this_cpu_cmpxchg_double().
> >  Now, this function gets called and we modify c->freelist, but cannot
> > get all objects and then fail (goto error).  Although we put-back
> > objects (via __kmem_cache_free_bulk) don't we want to update c->tid
> > in-order to make sure the call to this_cpu_cmpxchg_double() retry?
> 
> Hmm... I thought that __kmem_cache_free_bulk is run with interrupts
> disabled and will invoke the __slab_free which will increment tid if any
> objects are freed from the local page.

Ah, yes.  Fallback __kmem_cache_free_bulk() will invoke slab_free(),
which will have updated c->tid.  The patch is correct.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

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