When using IOB queue to store readahead data, we use one IOB for each
UDP packet. Then if the packets are very small, like 10Bytes per packet,
we'll use ~1600 IOBs just for 16KB recv buffer size, which is wasteful
and dangerous. So change conn->readahead to a single IOB chain like TCP.
Benefits:
- Using memory and IOBs more efficiently (small packets are common in
UDP)
Side effects:
- UDP recv buffer size may count the overhead
- A little bit drop in performance (<1%, more seek & copy)
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
075eb6a6d2