export: a kilobyte less a route advertised with all_paths; memory accounted for

A router feeding a collector every path (all_paths) was 4.8 GB resident
with a table that should take a third of that. A heap profile of the
daemon in the Linux VM, with four full tables and such a collector,
showed where it went: the exporter kept, for every route it had
advertised, the route's outgoing form, the parsed attribute list it was
dressed with, through an `Arc<Dressed>` in the per-route record. One
such form lived for every distinct attribute set advertised, about a
kilobyte each, for the life of the session, on top of the exporter's
cache of 262,144 of them. The record needs only to tell whether a route
changed, and the table's own attribute set, which is in memory anyway,
tells it that: the outgoing form is a function of the set, the peer the
route came from and the policy.

This change:

* `Sent` holds an `Arc<AttrSet>` instead of an `Arc<Dressed>`, and a
  route is sent again when its set differs. `Verdict::All` carries both
  while a flush is on.
* `DRESSED_KEPT` goes from 262,144 to 65,536: a kilobyte a set, so 64 MB
  rather than 256 MB a session at most; what a flush is sending holds
  its own.
* The status page's header shows the daemon's memory as jemalloc
  accounts for it (allocated and resident), `/api/status` has the six
  figures (`memory`: allocated, active, metadata, resident, mapped,
  retained), and `bgp_memory_bytes{kind}` exports them. jemalloc is built
  with statistics for this, and `bgp-web` reads them through
  `tikv-jemalloc-ctl`.
* `scripts/profile/full-table.sh` gains `COLLECTOR=1`, a collector
  session over IPv6 that takes both families with ADD-PATH, and `HEAP=1`,
  which builds the daemon with jemalloc's heap profiler (the new
  `heap-profiling` feature of the daemon crate, not for production) and
  turns the profile into a flame graph with jeprof; and it reports
  memory with the table in and again 30 s later. The feeder
  (`crates/bench/examples/feed.rs`) plays the collector with
  `FEED_COLLECTOR=1`.

Measured in the VM, four peers' full tables and a collector sent every
path (4.9 million routes advertised): 1,723 MiB resident before, 1,286
MiB after, with jemalloc's allocated figure from 1,500 MiB to 946 MiB.
Without the collector the same tables take 630 MiB, so the collector's
bookkeeping is now about 50 bytes a route advertised. Of the resident
figure, some 400 MiB was pages jemalloc had freed and not yet returned:
it returns them on allocator activity only, and a router that has its
tables in allocates little. jemalloc is now built with its background
thread on (the `background_threads` feature), which returns them on
time: 1,020 MiB resident 30 s after the load, against 1,286 MiB without
it.

Documentation: `memory` in the HTTP API reference, `bgp_memory_bytes`
in the metrics reference and the monitoring guide, the script's new
settings in the testing guide.

Testing: the ADD-PATH integration tests pass, including the collector
ones; the heap profile and the figures above are from
`PEERS=4 COLLECTOR=1 HEAP=1 scripts/profile/full-table.sh` in the VM.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/bench/examples/feed.rs

@@ -17,6 +17,12 @@
 //!   follow on from it.
 //! - `FEED_HOLD_SECS`: how long the sessions stay open after the table is
 //!   sent (default 30).
+//! - `FEED_COLLECTOR=1`: before the peers, one more session, as a route
+//!   collector would have: over IPv6, to `FEED_COLLECTOR_TO` (default
+//!   `[::1]:1790`) from `FEED_COLLECTOR_FROM` if set, offering to receive
+//!   several routes for a prefix (ADD-PATH) for both families and IPv4
+//!   routes with IPv6 next hops, and reading and dropping whatever it is
+//!   sent. Its AS number is 212232.
 //!
 //! What is printed: when the sessions are up and how long the writes took.
 //! The writes end when the kernel's socket buffers have taken the last
@@ -28,6 +34,9 @@ use std::time::{Duration, Instant};
 
 use bgp_bench::{Prefixes, Shape, announcements, encoded, env};
 use bgp_integration_tests::test_peer::TestPeer;
+use bgp_packet::open::{AddPathEntry, Capability, ExtendedNextHopEntry, SendReceive};
+use bgp_primitives::constants::{Afi, AfiSafi, Safi};
+use bgp_server::family::SUPPORTED;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::TcpSocket;
 use tokio::net::tcp::OwnedWriteHalf;
@@ -81,6 +90,61 @@ async fn main() {
         started.elapsed().as_secs_f64()
     );
 
+    // The collector first, so that it is there as the table arrives, as a
+    // router's collector session is after a restart.
+    let collector = env("FEED_COLLECTOR", 0) == 1;
+    let mut draining = Vec::new();
+    let mut collector_writer = None;
+    if collector {
+        let to: SocketAddr = std::env::var("FEED_COLLECTOR_TO")
+            .unwrap_or_else(|_| "[::1]:1790".into())
+            .parse()
+            .expect("FEED_COLLECTOR_TO is an IPv6 address and port");
+        let socket = TcpSocket::new_v6().expect("a socket");
+        if let Ok(from) = std::env::var("FEED_COLLECTOR_FROM") {
+            let address: std::net::Ipv6Addr = from.parse().expect("an IPv6 address");
+            socket
+                .bind(SocketAddr::new(address.into(), 0))
+                .expect("the collector's address is ours to connect from");
+        }
+        let stream = socket.connect(to).await.expect("the daemon listens");
+        let mut session = TestPeer::from_stream(stream);
+        let mut capabilities = vec![Capability::FourByteAsn { asn: 212_232 }];
+        capabilities.extend(SUPPORTED.into_iter().map(Capability::multiprotocol));
+        capabilities.push(Capability::AddPath {
+            entries: [AfiSafi::IPV4_UNICAST, AfiSafi::IPV6_UNICAST]
+                .into_iter()
+                .map(|family| AddPathEntry {
+                    afi: family.afi,
+                    safi: family.safi,
+                    send_recv: SendReceive::Receive,
+                })
+                .collect(),
+        });
+        capabilities.push(Capability::ExtendedNextHop {
+            entries: vec![ExtendedNextHopEntry {
+                afi: Afi::IPV4,
+                safi: Safi::UNICAST,
+                nh_afi: Afi::IPV6,
+            }],
+        });
+        session
+            .handshake_with(212_232, Ipv4Addr::new(10, 0, 0, 200), 90, capabilities)
+            .await
+            .expect("the daemon takes the collector's session");
+        let (mut reader, writer) = session.into_stream().into_split();
+        draining.push(tokio::spawn(async move {
+            let mut sink = [0u8; 65536];
+            while let Ok(n) = reader.read(&mut sink).await {
+                if n == 0 {
+                    break;
+                }
+            }
+        }));
+        println!("collector session established");
+        collector_writer = Some(writer);
+    }
+
     let mut sessions = Vec::new();
     for peer in 1..=peers {
         let socket = TcpSocket::new_v4().expect("a socket");
@@ -129,7 +193,7 @@ async fn main() {
             })
         })
         .collect();
-    let mut writers: Vec<OwnedWriteHalf> = Vec::new();
+    let mut writers: Vec<OwnedWriteHalf> = collector_writer.into_iter().collect();
     for (index, sender) in senders.into_iter().enumerate() {
         let (writer, took) = sender.await.expect("the sender runs");
         println!(
@@ -155,4 +219,5 @@ async fn main() {
         }
     }
     println!("sessions closed after {} s", hold.as_secs());
+    drop(draining);
 }