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