On 04/30/2012 11:10 AM, Eric Dumazet wrote: > From: Eric Dumazet <edumazet@xxxxxxxxxx> > > GRO can check if skb to be merged has its skb->head mapped to a page > fragment, instead of a kmalloc() area. > > We 'upgrade' skb->head as a fragment in itself > > This avoids the frag_list fallback, and permits to build true GRO skb > (one sk_buff and up to 16 fragments), using less memory. > > This reduces number of cache misses when user makes its copy, since a > single sk_buff is fetched. > > This is a followup of patch "net: allow skb->head to be a page fragment" > > Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> > Cc: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxx> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Cc: Maciej Żenczykowski <maze@xxxxxxxxxx> > Cc: Neal Cardwell <ncardwell@xxxxxxxxxx> > Cc: Tom Herbert <therbert@xxxxxxxxxx> > Cc: Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx> > Cc: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx> > Cc: Matt Carlson <mcarlson@xxxxxxxxxxxx> > Cc: Michael Chan <mchan@xxxxxxxxxxxx> > --- > > v2: change skb->head by skb->data to compute correct first_offset in > frag > > include/linux/netdevice.h | 2 ++ > include/linux/skbuff.h | 1 + > net/core/dev.c | 5 ++++- > net/core/skbuff.c | 27 ++++++++++++++++++++++++++- > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index e0b70e9..7f377fb 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -1509,6 +1509,8 @@ struct napi_gro_cb { > > /* Free the skb? */ > int free; > +#define NAPI_GRO_FREE 1 > +#define NAPI_GRO_FREE_STOLEN_HEAD 2 > }; > > #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb) > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 9d28a22..2c75e98 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -561,6 +561,7 @@ static inline struct rtable *skb_rtable(const struct sk_buff *skb) > extern void kfree_skb(struct sk_buff *skb); > extern void consume_skb(struct sk_buff *skb); > extern void __kfree_skb(struct sk_buff *skb); > +extern struct kmem_cache *skbuff_head_cache; > extern struct sk_buff *__alloc_skb(unsigned int size, > gfp_t priority, int fclone, int node); > extern struct sk_buff *build_skb(void *data, unsigned int frag_size); > diff --git a/net/core/dev.c b/net/core/dev.c > index 501f3cc..a2be59f 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -3546,7 +3546,10 @@ gro_result_t napi_skb_finish(gro_result_t ret, struct sk_buff *skb) > break; > > case GRO_MERGED_FREE: > - consume_skb(skb); > + if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD) > + kmem_cache_free(skbuff_head_cache, skb); > + else > + __kfree_skb(skb); > break; > > case GRO_HELD: How can you go from consume_skb() which checks for skb->users to a case that doesn't, or are you guaranteed that there is no way to get here with skb->users greater than 1? > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index effa75d..2ad1ee7 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -69,7 +69,7 @@ > #include <trace/events/skb.h> > #include <linux/highmem.h> > > -static struct kmem_cache *skbuff_head_cache __read_mostly; > +struct kmem_cache *skbuff_head_cache __read_mostly; > static struct kmem_cache *skbuff_fclone_cache __read_mostly; > > static void sock_pipe_buf_release(struct pipe_inode_info *pipe, > @@ -2901,6 +2901,31 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb) > > NAPI_GRO_CB(skb)->free = 1; > goto done; > + } else if (skb->head_frag) { > + int nr_frags = pinfo->nr_frags; > + skb_frag_t *frag = pinfo->frags + nr_frags; > + struct page *page = virt_to_head_page(skb->head); > + unsigned int first_size = headlen - offset; > + unsigned int first_offset; > + > + if (nr_frags + 1 + skbinfo->nr_frags > MAX_SKB_FRAGS) > + return -E2BIG; > + > + first_offset = skb->data - > + (unsigned char *)page_address(page) + > + offset; > + > + pinfo->nr_frags = nr_frags + 1 + skbinfo->nr_frags; > + > + frag->page.p = page; > + frag->page_offset = first_offset; > + skb_frag_size_set(frag, first_size); > + > + memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags); > + /* We dont need to clear skbinfo->nr_frags here */ > + > + NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD; > + goto done; > } else if (skb_gro_len(p) != pinfo->gso_size) > return -E2BIG; > > > Maybe I missed something, but shouldn't you be checking skb->cloned, and skb_shinfo()->dataref before you can consider just dropping the sk_buff? It seems like if you are sharing the frag with a clone you would have to retain the skb->head so that you can track the dataref. Otherwise you will likely cause issues because the stack could end up freeing the sk_buff, or the GRO frame will be capable of calling put_page and freeing the page out from under the clone. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html