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Fix excessive receive buffer allocation

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Allocation logic previously considered a GRO batch to be one datagram,
rather than (when supported) 64. This led to an unintended ~128MiB
allocation, now scaled back down to ~4MiB.
This commit is contained in:
Benjamin Saunders
2023-07-21 15:01:15 -07:00
parent 0ae7c60b15
commit 130de254ac
1 changed files with 23 additions and 11 deletions
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quinn/src/endpoint.rs
+23 -11
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@@ -384,20 +384,20 @@ pub(crate) struct Shared {
impl State {
fn drive_recv<'a>(&'a mut self, cx: &mut Context, now: Instant) -> Result<bool, io::Error> {
self.recv_limiter.start_cycle();
let recv_count = recv_datagram_count(&self.udp_state) / self.udp_state.gro_segments();
let mut metas = [RecvMeta::default(); BATCH_SIZE];
let mut iovs = MaybeUninit::<[IoSliceMut<'a>; BATCH_SIZE]>::uninit();
let mut iovs = std::array::from_fn::<MaybeUninit<IoSliceMut<'a>>, BATCH_SIZE, _>(|_| {
MaybeUninit::uninit()
});
self.recv_buf
.chunks_mut(self.recv_buf.len() / BATCH_SIZE)
.chunks_mut(self.recv_buf.len() / recv_count)
.enumerate()
.for_each(|(i, buf)| unsafe {
iovs.as_mut_ptr()
.cast::<IoSliceMut>()
.add(i)
.write(IoSliceMut::<'a>::new(buf));
.for_each(|(i, buf)| {
iovs[i].write(IoSliceMut::<'a>::new(buf));
});
let mut iovs = unsafe { iovs.assume_init() };
let iovs = unsafe { slice_assume_init_mut(&mut iovs[..recv_count]) };
loop {
match self.socket.poll_recv(cx, &mut iovs, &mut metas) {
match self.socket.poll_recv(cx, iovs, &mut metas) {
Poll::Ready(Ok(msgs)) => {
self.recv_limiter.record_work(msgs);
for (meta, buf) in metas.iter().zip(iovs.iter()).take(msgs) {
@@ -552,6 +552,12 @@ impl State {
}
}
// TODO: Remove once feature maybe_uninit_slice (https://github.com/rust-lang/rust/issues/63569)
// stabilizes
unsafe fn slice_assume_init_mut<T>(x: &mut [MaybeUninit<T>]) -> &mut [T] {
std::slice::from_raw_parts_mut(x.as_mut_ptr().cast(), x.len())
}
#[inline]
fn udp_transmit(t: proto::Transmit) -> udp::Transmit {
udp::Transmit {
@@ -673,8 +679,7 @@ impl EndpointRef {
let recv_buf = vec![
0;
inner.config().get_max_udp_payload_size().min(64 * 1024) as usize
* udp_state.gro_segments()
* BATCH_SIZE
* recv_datagram_count(&udp_state)
];
let (sender, events) = mpsc::unbounded_channel();
Self(Arc::new(EndpointInner {
@@ -737,3 +742,10 @@ impl std::ops::Deref for EndpointRef {
&self.0
}
}
/// Number of datagrams to allocate space for per recv
fn recv_datagram_count(udp: &UdpState) -> usize {
// We must receive in multiples of a GRO batch to avoid datagram truncation, and we want to
// accept at least `BATCH_SIZE` packets per receive.
usize::max(1, BATCH_SIZE / udp.gro_segments()) * udp.gro_segments()
}