Let the swap unit remain survive shutdown

Swap units have automatic dependencies of Before=swap.target,shutdown.target, Conflicts=shutdown.target. By adding DefaultDependencies=no, Before=swap.target, we effective drop the negative dependency with shutdown.target and allow the swap device to survive shutdown. There is no need to bring down the swap device during shutdown. This wastes work, because any remaning pages need to be dropped or decompressed and moved to normal memory. Normally this is very quick, but the report says that it takes 15–20 seconds in their case. Closes #191.
systemd · Nov 21, 2024 · d69ff7b · d69ff7b
1 parent 597d429
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diff --git a/src/generator.rs b/src/generator.rs
@@ -226,8 +226,12 @@ fn handle_zram_swap(output_directory: &Path, device: &Device) -> Result<()> {
 [Unit]
 Description=Compressed Swap on /dev/{zram_device}
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 Requires=systemd-zram-setup@{zram_device}.service
 After=systemd-zram-setup@{zram_device}.service
+Before=swap.target
 
 [Swap]
 What=/dev/{zram_device}

diff --git a/tests/01-basic/run.expected/units/dev-zram0.swap b/tests/01-basic/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/02-zstd/run.expected/units/dev-zram0.swap b/tests/02-zstd/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/04-dropins/run.expected/units/dev-zram0.swap b/tests/04-dropins/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/04-dropins/run.expected/units/dev-zram2.swap b/tests/04-dropins/run.expected/units/dev-zram2.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram2
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram2

diff --git a/tests/06-kernel-enabled/run.expected/units/dev-zram0.swap b/tests/06-kernel-enabled/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/09-zram-size/run.expected/units/dev-zram0.swap b/tests/09-zram-size/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/10-example/run.expected/units/dev-zram0.swap b/tests/10-example/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/11-obsolete/run.expected/units/dev-zram0.swap b/tests/11-obsolete/run.expected/units/dev-zram0.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram0
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram0

diff --git a/tests/11-obsolete/run.expected/units/dev-zram1.swap b/tests/11-obsolete/run.expected/units/dev-zram1.swap
@@ -3,8 +3,12 @@
 [Unit]
 Description=Compressed Swap on /dev/zram1
 Documentation=man:zram-generator(8) man:zram-generator.conf(5)
+
+DefaultDependencies=no
+
 [email protected]
 [email protected]
+Before=swap.target
 
 [Swap]
 What=/dev/zram1