On Fri, 4 Sep 2015 11:47:17 -0700 Tom Herbert <tom@xxxxxxxxxxxxxxx> wrote:
> On Fri, Sep 4, 2015 at 10:00 AM, Jesper Dangaard Brouer <brouer@xxxxxxxxxx> wrote:
> > Introduce the first user of SLAB bulk free API kmem_cache_free_bulk(),
> > in the network stack in form of function kfree_skb_bulk() which bulk
> > free SKBs (not skb clones or skb->head, yet).
> >
[...]
> > +/**
> > + * kfree_skb_bulk - bulk free SKBs when refcnt allows to
> > + * @skbs: array of SKBs to free
> > + * @size: number of SKBs in array
> > + *
> > + * If SKB refcnt allows for free, then release any auxiliary data
> > + * and then bulk free SKBs to the SLAB allocator.
> > + *
> > + * Note that interrupts must be enabled when calling this function.
> > + */
> > +void kfree_skb_bulk(struct sk_buff **skbs, unsigned int size)
> > +{
>
> What not pass a list of skbs (e.g. using skb->next)?
Because the next layer, the slab API needs an array:
kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
Look at the patch:
[PATCH V2 3/3] slub: build detached freelist with look-ahead
http://thread.gmane.org/gmane.linux.kernel.mm/137469/focus=137472
Where I use this array to progressively scan for objects belonging to
the same page. (A subtle detail is I manage to zero out the array,
which is good from a security/error-handling point of view, as pointers
to the objects are not left dangling on the stack).
I cannot argue that, writing skb->next comes as an additional cost,
because the slUb free also writes into this cacheline. Perhaps the
slAb allocator does not?
[...]
> > + if (likely(cnt)) {
> > + kmem_cache_free_bulk(skbuff_head_cache, cnt, (void **) skbs);
> > + }
> > +}
> > +EXPORT_SYMBOL(kfree_skb_bulk);
--
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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