Re: [Xen-devel] [PATCH net-next v4 6/9] xen-netback: Handle guests with too many frags

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 16/01/14 00:03, Wei Liu wrote:
> On Tue, Jan 14, 2014 at 08:39:52PM +0000, Zoltan Kiss wrote:
> [...]
> >         /* Skip first skb fragment if it is on same page as header fragment. */
> > @@ -832,6 +851,29 @@ static struct gnttab_map_grant_ref 
> > *xenvif_get_requests(struct xenvif *vif,
> >
> >         BUG_ON(shinfo->nr_frags > MAX_SKB_FRAGS);
> >
> > +       if (frag_overflow) {
> > +               struct sk_buff *nskb = xenvif_alloc_skb(0);
> > +               if (unlikely(nskb == NULL)) {
> > +                       netdev_err(vif->dev,
> > +                                  "Can't allocate the frag_list skb.\n");
> This, and other occurences of netdev_* logs need to be rate limit.
> Otherwise you risk flooding kernel log when system is under memory
> pressure.
Done.

> > @@ -1537,6 +1613,32 @@ static int xenvif_tx_submit(struct xenvif *vif)
> >                                   pending_idx :
> >                                   INVALID_PENDING_IDX);
> >
> > +               if (skb_shinfo(skb)->frag_list) {
> > +                       nskb = skb_shinfo(skb)->frag_list;
> > +                       xenvif_fill_frags(vif, nskb, INVALID_PENDING_IDX);
> > +                       skb->len += nskb->len;
> > +                       skb->data_len += nskb->len;
> > +                       skb->truesize += nskb->truesize;
> > +                       skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> > +                       skb_shinfo(nskb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> > +                       vif->tx_zerocopy_sent += 2;
> > +                       nskb = skb;
> > +
> > +                       skb = skb_copy_expand(skb,
> > +                                             0,
> > +                                             0,
> > +                                             GFP_ATOMIC | __GFP_NOWARN);
> > +                       if (!skb) {
> > +                               netdev_dbg(vif->dev,
> > +                                          "Can't consolidate skb with too many 
> > fragments\n");
> Rate limit.
>
> > +                               if (skb_shinfo(nskb)->destructor_arg)
> > +                                       skb_shinfo(nskb)->tx_flags |=
> > +                                               SKBTX_DEV_ZEROCOPY;
> Why is this needed? nskb is the saved pointer to original skb, which has
> already had SKBTX_DEV_ZEROCOPY in tx_flags. Did I miss something?
Indeed. This actually belongs to the header grant copy patches I've sent 
in as well. I move it there.

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