[PATCH] listener: don't set listen backlog on inherited sockets

[Eric Wong <e@80x24.org>]

Eric Wong <e@80x24.org> wrote:
> I wonder if prioritizing certain User-Agents (e.g. curl, w3m,
> anything with non-Anroid "Linux" in it) would be a quick fix in
> haproxy||nginx.

This seems like a long overdue change to allow certain listen
sockets to handle more traffic than others.

---------8<-------
Subject: [PATCH] listener: don't set listen backlog on inherited sockets

By using the listen(2) backlog as-is when inheriting (from
systemd or similar), we can give the sysadmin more control on
controlling overload on a per-listener basis.  For systemd
users, this means the `Backlog=' parameter in systemd.socket(5)
can be respected and configured to give certain sockets a
smaller backlog (perhaps combined with with per-listener
`multi-accept' parameter on sockets with the standard (huge)
backlog).

For sockets we create, continue to use INT_MAX and let the
kernel clamp it to whatever system-wide limit there is
(e.g. `net.core.somaxconn' sysctl on Linux).
---
 lib/PublicInbox/Daemon.pm   | 2 +-
 lib/PublicInbox/LEI.pm      | 3 ++-
 lib/PublicInbox/Listener.pm | 1 -
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/Daemon.pm b/lib/PublicInbox/Daemon.pm
index 5d93f81f..8fe93acd 100644
--- a/lib/PublicInbox/Daemon.pm
+++ b/lib/PublicInbox/Daemon.pm
@@ -264,7 +264,7 @@ EOF
 			die $@ if $@;
 			%o = (LocalAddr => $l, ReuseAddr => 1, Proto => 'tcp');
 		}
-		$o{Listen} = 1024;
+		$o{Listen} = 2**31 - 1; # kernel will clamp
 		my $prev = umask 0000;
 		my $s = eval { $sock_pkg->new(%o) } or
 			warn "error binding $l: $! ($@)\n";
diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index 94bac688..0a779c4f 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -9,7 +9,7 @@ package PublicInbox::LEI;
 use v5.12;
 use parent qw(PublicInbox::DS PublicInbox::LeiExternal
 	PublicInbox::LeiQuery);
-use autodie qw(bind chdir open pipe socket socketpair syswrite unlink);
+use autodie qw(bind chdir listen open pipe socket socketpair syswrite unlink);
 use Getopt::Long ();
 use Socket qw(AF_UNIX SOCK_SEQPACKET pack_sockaddr_un);
 use Errno qw(EPIPE EAGAIN ECONNREFUSED ENOENT ECONNRESET EINTR);
@@ -1371,6 +1371,7 @@ sub lazy_start {
 	local (%PATH2CFG, $MDIR2CFGPATH);
 	local $daemon_pid = $$;
 	$listener->blocking(0);
+	listen $listener, 2**31 - 1; # kernel will clamp
 	my $exit_code;
 	my $pil = PublicInbox::Listener->new($listener, \&accept_dispatch);
 	local $quit = do {
diff --git a/lib/PublicInbox/Listener.pm b/lib/PublicInbox/Listener.pm
index c83901b2..62475600 100644
--- a/lib/PublicInbox/Listener.pm
+++ b/lib/PublicInbox/Listener.pm
@@ -21,7 +21,6 @@ sub new {
 	my ($class, $s, $cb, $multi_accept) = @_;
 	setsockopt($s, SOL_SOCKET, SO_KEEPALIVE, 1);
 	setsockopt($s, IPPROTO_TCP, TCP_NODELAY, 1); # ignore errors on non-TCP
-	listen($s, 2**31 - 1); # kernel will clamp
 	my $self = bless { post_accept => $cb }, $class;
 	$self->{multi_accept} = $multi_accept //= $MULTI_ACCEPT;
 	$self->SUPER::new($s, EPOLLIN|EPOLLEXCLUSIVE);