systemd: add patch to increase mount rate limit

Bottlerocket includes a lot of mount units, and the 5 mounts/s rate limit leads to several throttles during the boot process. The higher rate limit eliminates this, speeding up the boot by up to one second. Setting `SYSTEMD_DEFAULT_MOUNT_RATE_LIMIT_BURST` in the environment can also change the rate limit, but this must be done on the kernel command line. If we set it there by default, then it can't be tuned by system administrators using `settings.boot.kernel-parameters`. Signed-off-by: Ben Cressey <[email protected]>
bottlerocket-os · Aug 31, 2023 · 6f17ad7 · 6f17ad7
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diff --git a/packages/systemd/9012-core-mount-increase-mount-rate-limit-burst-to-25.patch b/packages/systemd/9012-core-mount-increase-mount-rate-limit-burst-to-25.patch
@@ -0,0 +1,29 @@
+From 1f8d86a74c09738eb000aacec6bbd74360177796 Mon Sep 17 00:00:00 2001
+From: Ben Cressey <[email protected]>
+Date: Thu, 31 Aug 2023 19:14:13 +0000
+Subject: [PATCH] core/mount: increase mount rate limit burst to 25
+
+On systems where many mounts are set up on boot, the default rate
+limit is too low and leads to several stalls.
+
+Signed-off-by: Ben Cressey <[email protected]>
+---
+ src/core/mount.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/core/mount.c b/src/core/mount.c
+index d82092a..7ba009b 100644
+--- a/src/core/mount.c
++++ b/src/core/mount.c
+@@ -1928,7 +1928,7 @@ static void mount_enumerate(Manager *m) {
+         mnt_init_debug(0);
+
+         if (!m->mount_monitor) {
+-                unsigned mount_rate_limit_burst = 5;
++                unsigned mount_rate_limit_burst = 25;
+                 int fd;
+
+                 m->mount_monitor = mnt_new_monitor();
+-- 
+2.40.1
+
diff --git a/packages/systemd/systemd.spec b/packages/systemd/systemd.spec
@@ -52,6 +52,11 @@ Patch9010: 9010-units-keep-modprobe-service-units-running.patch
 # DBUS services not used in Bottlerocket
 Patch9011: 9011-systemd-networkd-Conditionalize-hostnamed-timezoned-.patch
 
+# Local patch to adjust the default mount rate limit to 25 per second.
+# Carried as a patch so that SYSTEMD_DEFAULT_MOUNT_RATE_LIMIT_BURST can be used
+# as a kernel command line parameter to override.
+Patch9012: 9012-core-mount-increase-mount-rate-limit-burst-to-25.patch
+
 BuildRequires: gperf
 BuildRequires: intltool
 BuildRequires: meson