How to use swap space for emergencies only?
I have a Debian (Buster) laptop with 8GB ram and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past 6 days while it churns through.
While doing this I periodically need to use my laptop as a laptop. This shouldn't be a problem, the long running task is IO bound working through stuff on a USB hard disk and doesn't take much RAM (<200MB) or CPU (<4%).
The problem is when I come back to my laptop after a few hours, it will be very sluggish and can take 30 minutes to come back to normal. This is so bad that crash-monitors flag their respective apps as having frozen (especially browser windows) and things start incorrectly crashing out.
Looking on the system monitor, of the 2.5GB used around half gets shifted into swap. I've confirmed this is the problem by removing the swap space (swapoff /dev/sda8
). If I leave it without swap space it comes back to life almost instantly even after 24 hours. With swap, it's practically a brick for the first 5 minutes having been left for only 6 hours. I've confirmed that memory usage never exceeds 3GB even while I'm away.
I have tried reducing the swappiness (see also: wikipedia) to values of 10
and 0
, but the problem still persists. It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk). The long running task is reading through a vast file tree and reading every file. So it might be the kernel is confused into thinking that caching would help. But on single sweep of a 2TB USB HD with ~1 billion file names, an extra GB RAM isn't going to help performance much. This is a cheap laptop with a sluggish hard drive. It simply can't load data back into RAM fast enough.
How can I tell linux to only use swap space in an emergency? I don't want to run without swap. If something unexpected happens, and the OS suddenly needs and extra few GB then I don't want tasks to get killed and would prefer start using swap. But at the moment, if I leave swap enabled, my laptop just can't be used when I need it.
The precise definition of an "emergency" might be a matter for debate. But to clarify what I mean: An emergency would be where the system is left without any other option than to swap or kill processes.
What is an emergency? - Do you really have to ask?... I hope you never find yourself in a burning building!
It's not possible for me to define everything that might constitute an emergency in this question. But for example, an emergency might be when the kernel is so pushed for memory that it has start killing processes with the OOM Killer. An emergency is NOT when the kernel thinks it can improve performance by using swap.
linux debian kernel swap
|
show 1 more comment
I have a Debian (Buster) laptop with 8GB ram and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past 6 days while it churns through.
While doing this I periodically need to use my laptop as a laptop. This shouldn't be a problem, the long running task is IO bound working through stuff on a USB hard disk and doesn't take much RAM (<200MB) or CPU (<4%).
The problem is when I come back to my laptop after a few hours, it will be very sluggish and can take 30 minutes to come back to normal. This is so bad that crash-monitors flag their respective apps as having frozen (especially browser windows) and things start incorrectly crashing out.
Looking on the system monitor, of the 2.5GB used around half gets shifted into swap. I've confirmed this is the problem by removing the swap space (swapoff /dev/sda8
). If I leave it without swap space it comes back to life almost instantly even after 24 hours. With swap, it's practically a brick for the first 5 minutes having been left for only 6 hours. I've confirmed that memory usage never exceeds 3GB even while I'm away.
I have tried reducing the swappiness (see also: wikipedia) to values of 10
and 0
, but the problem still persists. It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk). The long running task is reading through a vast file tree and reading every file. So it might be the kernel is confused into thinking that caching would help. But on single sweep of a 2TB USB HD with ~1 billion file names, an extra GB RAM isn't going to help performance much. This is a cheap laptop with a sluggish hard drive. It simply can't load data back into RAM fast enough.
How can I tell linux to only use swap space in an emergency? I don't want to run without swap. If something unexpected happens, and the OS suddenly needs and extra few GB then I don't want tasks to get killed and would prefer start using swap. But at the moment, if I leave swap enabled, my laptop just can't be used when I need it.
The precise definition of an "emergency" might be a matter for debate. But to clarify what I mean: An emergency would be where the system is left without any other option than to swap or kill processes.
What is an emergency? - Do you really have to ask?... I hope you never find yourself in a burning building!
It's not possible for me to define everything that might constitute an emergency in this question. But for example, an emergency might be when the kernel is so pushed for memory that it has start killing processes with the OOM Killer. An emergency is NOT when the kernel thinks it can improve performance by using swap.
linux debian kernel swap
6
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
1
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
1
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
1
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
1
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago
|
show 1 more comment
I have a Debian (Buster) laptop with 8GB ram and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past 6 days while it churns through.
While doing this I periodically need to use my laptop as a laptop. This shouldn't be a problem, the long running task is IO bound working through stuff on a USB hard disk and doesn't take much RAM (<200MB) or CPU (<4%).
The problem is when I come back to my laptop after a few hours, it will be very sluggish and can take 30 minutes to come back to normal. This is so bad that crash-monitors flag their respective apps as having frozen (especially browser windows) and things start incorrectly crashing out.
Looking on the system monitor, of the 2.5GB used around half gets shifted into swap. I've confirmed this is the problem by removing the swap space (swapoff /dev/sda8
). If I leave it without swap space it comes back to life almost instantly even after 24 hours. With swap, it's practically a brick for the first 5 minutes having been left for only 6 hours. I've confirmed that memory usage never exceeds 3GB even while I'm away.
I have tried reducing the swappiness (see also: wikipedia) to values of 10
and 0
, but the problem still persists. It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk). The long running task is reading through a vast file tree and reading every file. So it might be the kernel is confused into thinking that caching would help. But on single sweep of a 2TB USB HD with ~1 billion file names, an extra GB RAM isn't going to help performance much. This is a cheap laptop with a sluggish hard drive. It simply can't load data back into RAM fast enough.
How can I tell linux to only use swap space in an emergency? I don't want to run without swap. If something unexpected happens, and the OS suddenly needs and extra few GB then I don't want tasks to get killed and would prefer start using swap. But at the moment, if I leave swap enabled, my laptop just can't be used when I need it.
The precise definition of an "emergency" might be a matter for debate. But to clarify what I mean: An emergency would be where the system is left without any other option than to swap or kill processes.
What is an emergency? - Do you really have to ask?... I hope you never find yourself in a burning building!
It's not possible for me to define everything that might constitute an emergency in this question. But for example, an emergency might be when the kernel is so pushed for memory that it has start killing processes with the OOM Killer. An emergency is NOT when the kernel thinks it can improve performance by using swap.
linux debian kernel swap
I have a Debian (Buster) laptop with 8GB ram and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past 6 days while it churns through.
While doing this I periodically need to use my laptop as a laptop. This shouldn't be a problem, the long running task is IO bound working through stuff on a USB hard disk and doesn't take much RAM (<200MB) or CPU (<4%).
The problem is when I come back to my laptop after a few hours, it will be very sluggish and can take 30 minutes to come back to normal. This is so bad that crash-monitors flag their respective apps as having frozen (especially browser windows) and things start incorrectly crashing out.
Looking on the system monitor, of the 2.5GB used around half gets shifted into swap. I've confirmed this is the problem by removing the swap space (swapoff /dev/sda8
). If I leave it without swap space it comes back to life almost instantly even after 24 hours. With swap, it's practically a brick for the first 5 minutes having been left for only 6 hours. I've confirmed that memory usage never exceeds 3GB even while I'm away.
I have tried reducing the swappiness (see also: wikipedia) to values of 10
and 0
, but the problem still persists. It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk). The long running task is reading through a vast file tree and reading every file. So it might be the kernel is confused into thinking that caching would help. But on single sweep of a 2TB USB HD with ~1 billion file names, an extra GB RAM isn't going to help performance much. This is a cheap laptop with a sluggish hard drive. It simply can't load data back into RAM fast enough.
How can I tell linux to only use swap space in an emergency? I don't want to run without swap. If something unexpected happens, and the OS suddenly needs and extra few GB then I don't want tasks to get killed and would prefer start using swap. But at the moment, if I leave swap enabled, my laptop just can't be used when I need it.
The precise definition of an "emergency" might be a matter for debate. But to clarify what I mean: An emergency would be where the system is left without any other option than to swap or kill processes.
What is an emergency? - Do you really have to ask?... I hope you never find yourself in a burning building!
It's not possible for me to define everything that might constitute an emergency in this question. But for example, an emergency might be when the kernel is so pushed for memory that it has start killing processes with the OOM Killer. An emergency is NOT when the kernel thinks it can improve performance by using swap.
linux debian kernel swap
linux debian kernel swap
edited 4 hours ago
Philip Couling
asked 13 hours ago
Philip CoulingPhilip Couling
700415
700415
6
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
1
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
1
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
1
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
1
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago
|
show 1 more comment
6
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
1
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
1
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
1
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
1
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago
6
6
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
1
1
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
1
1
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
1
1
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
1
1
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago
|
show 1 more comment
5 Answers
5
active
oldest
votes
One fix is to make sure the memory cgroup controller is enabled (I think it is by default in even half-recent kernels, otherwise you'll need to add cgroup_enable=memory
to the kernel command line). Then you can run your I/O intensive task in a cgroup with a memory limit, which also limits the amount of cache it can consume.
If you're using systemd, you can set +MemoryAccounting=yes
and either MemoryHigh
/MemoryMax
or MemoryLimit
(depeneds on if you're using cgroup v1 or v2) in the unit, or a slice containing it. If its a slice, you can use systemd-run
to run the program in the slice.
Full example from one of my systems for running Firefox with a memory limit. Note this uses cgroups v2 and is set up as my user, not root (one of the advantages of v2 over v1 is that delegating this to non-root is safe, so systemd does it).
$ systemctl --user cat mozilla.slice
# /home/anthony/.config/systemd/user/mozilla.slice
[Unit]
Description=Slice for Mozilla apps
Before=slices.target
[Slice]
MemoryAccounting=yes
MemoryHigh=5G
MemoryMax=6G
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/firefox &
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/thunderbird &
I found to get the user one working I had to use a slice. System one works just by putting the options in the service file (or using systemctl set-property
on the service).
Here is an example service (using cgroup v1), note the last two lines. This is part of the system (pid=1) instance.
[Unit]
Description=mount S3QL filesystem
Requires=network-online.target
After=network-online.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=s3ql-user
Group=s3ql-user
LimitNOFILE=20000
ExecStartPre=+/bin/sh -c 'printf "S3QL_CACHE_SIZE=%%in" $(stat -c "%%a*%%S*.90/1024" -f /srv/s3ql-cache/ | bc) > /run/local-s3ql-env'
ExecStartPre=/usr/bin/fsck.s3ql --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --log none «REDACTED»
EnvironmentFile=-/run/local-s3ql-env
ExecStart=/usr/bin/mount.s3ql --keep-cache --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --cachesize ${S3QL_CACHE_SIZE} --threads 4
ExecStop=/usr/bin/umount.s3ql /mnt/S3QL/
TimeoutStopSec=2m
MemoryAccounting=yes
MemoryLimit=1G
Documentation is in systemd.resource-control(5)
.
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
add a comment |
It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk).
The kernel is doing The Right Thing™ believing it. Why would it keep in RAM unused memory and so essentially waste it instead of using it as cache or something?
I don't think the Linux kernel is gratuitously or anticipatory swapping out pages so if it does it, that must be to store something else on RAM, thus improving performance.
If you know when you'll need to reuse your laptop in advance, you might use the at
command (or crontab
) to schedule a swap cleanup (swapoff -a
).
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
add a comment |
Here's an idea, which I haven't tried myself (and I'm sorry I haven't the time right now to experiment with this).
Suppose you create a small VM with only 512MB memory for your background process I'm not sure if you'd want this to have any swap, your call, and switch off swap on your host system.
add a comment |
Is the process you're running something you've created yourself?
If so, it might be worth tweaking your code to open the files using the O_DIRECT
flag, which to quote the manual page -
Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT. See NOTES below for further discussion.
add a comment |
Remove swap or diminish it about 20% (may vary with systems) as recently OS are not using swap anymore the same way as they did in the few years ago. It probably answer some of your question:
here --> official redhat.com
important info:
In the past, some application vendors recommended swap of a size equal to
the RAM, or even twice the RAM. Now let us imagine the above-mentioned
system with 2GB of RAM and 2GB of swap. A database on the system was by
mistake configured for a system with 5GB of RAM. Once the physical memory is
used up, swap gets used. As the swap disk is much slower than RAM, the
performance goes down, and thrashing occurs. At this point, even logins into
the system might become impossible. As more and more memory gets written to,
eventually both physical- and swap memory are completely exhausted and the
OOM killer kicks in, killing one or more processes. In our case, quite a lot
of swap is available, so the time of poor performance is long.
and
https://wiki.debian.org/Swap
small portion of link above:
Information and considerations related to the amount of swap to use:
"The recommended amount of swap space has traditionally been double the amount of
system memory. This has changed over time to one and half times system memory, both
answers are decent baselines but are becoming less and less useful answers to the
question as time passes. There are many variables about your system and intended use
that will determine the available system swap you will want to have."
You may try:
Best way to disable swap in linux
Personal note:
Since I've 6GB RAM and in all my recently Linux OS. I've never ever seem any indication of use of Swap. I determined it I must turn it off either for space (few gigs more) and because it has slowered my system sometimes.
New contributor
add a comment |
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5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
One fix is to make sure the memory cgroup controller is enabled (I think it is by default in even half-recent kernels, otherwise you'll need to add cgroup_enable=memory
to the kernel command line). Then you can run your I/O intensive task in a cgroup with a memory limit, which also limits the amount of cache it can consume.
If you're using systemd, you can set +MemoryAccounting=yes
and either MemoryHigh
/MemoryMax
or MemoryLimit
(depeneds on if you're using cgroup v1 or v2) in the unit, or a slice containing it. If its a slice, you can use systemd-run
to run the program in the slice.
Full example from one of my systems for running Firefox with a memory limit. Note this uses cgroups v2 and is set up as my user, not root (one of the advantages of v2 over v1 is that delegating this to non-root is safe, so systemd does it).
$ systemctl --user cat mozilla.slice
# /home/anthony/.config/systemd/user/mozilla.slice
[Unit]
Description=Slice for Mozilla apps
Before=slices.target
[Slice]
MemoryAccounting=yes
MemoryHigh=5G
MemoryMax=6G
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/firefox &
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/thunderbird &
I found to get the user one working I had to use a slice. System one works just by putting the options in the service file (or using systemctl set-property
on the service).
Here is an example service (using cgroup v1), note the last two lines. This is part of the system (pid=1) instance.
[Unit]
Description=mount S3QL filesystem
Requires=network-online.target
After=network-online.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=s3ql-user
Group=s3ql-user
LimitNOFILE=20000
ExecStartPre=+/bin/sh -c 'printf "S3QL_CACHE_SIZE=%%in" $(stat -c "%%a*%%S*.90/1024" -f /srv/s3ql-cache/ | bc) > /run/local-s3ql-env'
ExecStartPre=/usr/bin/fsck.s3ql --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --log none «REDACTED»
EnvironmentFile=-/run/local-s3ql-env
ExecStart=/usr/bin/mount.s3ql --keep-cache --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --cachesize ${S3QL_CACHE_SIZE} --threads 4
ExecStop=/usr/bin/umount.s3ql /mnt/S3QL/
TimeoutStopSec=2m
MemoryAccounting=yes
MemoryLimit=1G
Documentation is in systemd.resource-control(5)
.
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
add a comment |
One fix is to make sure the memory cgroup controller is enabled (I think it is by default in even half-recent kernels, otherwise you'll need to add cgroup_enable=memory
to the kernel command line). Then you can run your I/O intensive task in a cgroup with a memory limit, which also limits the amount of cache it can consume.
If you're using systemd, you can set +MemoryAccounting=yes
and either MemoryHigh
/MemoryMax
or MemoryLimit
(depeneds on if you're using cgroup v1 or v2) in the unit, or a slice containing it. If its a slice, you can use systemd-run
to run the program in the slice.
Full example from one of my systems for running Firefox with a memory limit. Note this uses cgroups v2 and is set up as my user, not root (one of the advantages of v2 over v1 is that delegating this to non-root is safe, so systemd does it).
$ systemctl --user cat mozilla.slice
# /home/anthony/.config/systemd/user/mozilla.slice
[Unit]
Description=Slice for Mozilla apps
Before=slices.target
[Slice]
MemoryAccounting=yes
MemoryHigh=5G
MemoryMax=6G
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/firefox &
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/thunderbird &
I found to get the user one working I had to use a slice. System one works just by putting the options in the service file (or using systemctl set-property
on the service).
Here is an example service (using cgroup v1), note the last two lines. This is part of the system (pid=1) instance.
[Unit]
Description=mount S3QL filesystem
Requires=network-online.target
After=network-online.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=s3ql-user
Group=s3ql-user
LimitNOFILE=20000
ExecStartPre=+/bin/sh -c 'printf "S3QL_CACHE_SIZE=%%in" $(stat -c "%%a*%%S*.90/1024" -f /srv/s3ql-cache/ | bc) > /run/local-s3ql-env'
ExecStartPre=/usr/bin/fsck.s3ql --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --log none «REDACTED»
EnvironmentFile=-/run/local-s3ql-env
ExecStart=/usr/bin/mount.s3ql --keep-cache --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --cachesize ${S3QL_CACHE_SIZE} --threads 4
ExecStop=/usr/bin/umount.s3ql /mnt/S3QL/
TimeoutStopSec=2m
MemoryAccounting=yes
MemoryLimit=1G
Documentation is in systemd.resource-control(5)
.
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
add a comment |
One fix is to make sure the memory cgroup controller is enabled (I think it is by default in even half-recent kernels, otherwise you'll need to add cgroup_enable=memory
to the kernel command line). Then you can run your I/O intensive task in a cgroup with a memory limit, which also limits the amount of cache it can consume.
If you're using systemd, you can set +MemoryAccounting=yes
and either MemoryHigh
/MemoryMax
or MemoryLimit
(depeneds on if you're using cgroup v1 or v2) in the unit, or a slice containing it. If its a slice, you can use systemd-run
to run the program in the slice.
Full example from one of my systems for running Firefox with a memory limit. Note this uses cgroups v2 and is set up as my user, not root (one of the advantages of v2 over v1 is that delegating this to non-root is safe, so systemd does it).
$ systemctl --user cat mozilla.slice
# /home/anthony/.config/systemd/user/mozilla.slice
[Unit]
Description=Slice for Mozilla apps
Before=slices.target
[Slice]
MemoryAccounting=yes
MemoryHigh=5G
MemoryMax=6G
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/firefox &
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/thunderbird &
I found to get the user one working I had to use a slice. System one works just by putting the options in the service file (or using systemctl set-property
on the service).
Here is an example service (using cgroup v1), note the last two lines. This is part of the system (pid=1) instance.
[Unit]
Description=mount S3QL filesystem
Requires=network-online.target
After=network-online.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=s3ql-user
Group=s3ql-user
LimitNOFILE=20000
ExecStartPre=+/bin/sh -c 'printf "S3QL_CACHE_SIZE=%%in" $(stat -c "%%a*%%S*.90/1024" -f /srv/s3ql-cache/ | bc) > /run/local-s3ql-env'
ExecStartPre=/usr/bin/fsck.s3ql --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --log none «REDACTED»
EnvironmentFile=-/run/local-s3ql-env
ExecStart=/usr/bin/mount.s3ql --keep-cache --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --cachesize ${S3QL_CACHE_SIZE} --threads 4
ExecStop=/usr/bin/umount.s3ql /mnt/S3QL/
TimeoutStopSec=2m
MemoryAccounting=yes
MemoryLimit=1G
Documentation is in systemd.resource-control(5)
.
One fix is to make sure the memory cgroup controller is enabled (I think it is by default in even half-recent kernels, otherwise you'll need to add cgroup_enable=memory
to the kernel command line). Then you can run your I/O intensive task in a cgroup with a memory limit, which also limits the amount of cache it can consume.
If you're using systemd, you can set +MemoryAccounting=yes
and either MemoryHigh
/MemoryMax
or MemoryLimit
(depeneds on if you're using cgroup v1 or v2) in the unit, or a slice containing it. If its a slice, you can use systemd-run
to run the program in the slice.
Full example from one of my systems for running Firefox with a memory limit. Note this uses cgroups v2 and is set up as my user, not root (one of the advantages of v2 over v1 is that delegating this to non-root is safe, so systemd does it).
$ systemctl --user cat mozilla.slice
# /home/anthony/.config/systemd/user/mozilla.slice
[Unit]
Description=Slice for Mozilla apps
Before=slices.target
[Slice]
MemoryAccounting=yes
MemoryHigh=5G
MemoryMax=6G
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/firefox &
$ systemd-run --user --slice mozilla.slice --scope -- /usr/bin/thunderbird &
I found to get the user one working I had to use a slice. System one works just by putting the options in the service file (or using systemctl set-property
on the service).
Here is an example service (using cgroup v1), note the last two lines. This is part of the system (pid=1) instance.
[Unit]
Description=mount S3QL filesystem
Requires=network-online.target
After=network-online.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=s3ql-user
Group=s3ql-user
LimitNOFILE=20000
ExecStartPre=+/bin/sh -c 'printf "S3QL_CACHE_SIZE=%%in" $(stat -c "%%a*%%S*.90/1024" -f /srv/s3ql-cache/ | bc) > /run/local-s3ql-env'
ExecStartPre=/usr/bin/fsck.s3ql --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --log none «REDACTED»
EnvironmentFile=-/run/local-s3ql-env
ExecStart=/usr/bin/mount.s3ql --keep-cache --cachedir /srv/s3ql-cache/fs1 --authfile /etc/s3ql-authinfo --cachesize ${S3QL_CACHE_SIZE} --threads 4
ExecStop=/usr/bin/umount.s3ql /mnt/S3QL/
TimeoutStopSec=2m
MemoryAccounting=yes
MemoryLimit=1G
Documentation is in systemd.resource-control(5)
.
edited 10 hours ago
answered 11 hours ago
derobertderobert
73.5k8156211
73.5k8156211
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
add a comment |
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
@sourcejedi sounds right, I'll add a note.
– derobert
11 hours ago
add a comment |
It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk).
The kernel is doing The Right Thing™ believing it. Why would it keep in RAM unused memory and so essentially waste it instead of using it as cache or something?
I don't think the Linux kernel is gratuitously or anticipatory swapping out pages so if it does it, that must be to store something else on RAM, thus improving performance.
If you know when you'll need to reuse your laptop in advance, you might use the at
command (or crontab
) to schedule a swap cleanup (swapoff -a
).
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
add a comment |
It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk).
The kernel is doing The Right Thing™ believing it. Why would it keep in RAM unused memory and so essentially waste it instead of using it as cache or something?
I don't think the Linux kernel is gratuitously or anticipatory swapping out pages so if it does it, that must be to store something else on RAM, thus improving performance.
If you know when you'll need to reuse your laptop in advance, you might use the at
command (or crontab
) to schedule a swap cleanup (swapoff -a
).
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
add a comment |
It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk).
The kernel is doing The Right Thing™ believing it. Why would it keep in RAM unused memory and so essentially waste it instead of using it as cache or something?
I don't think the Linux kernel is gratuitously or anticipatory swapping out pages so if it does it, that must be to store something else on RAM, thus improving performance.
If you know when you'll need to reuse your laptop in advance, you might use the at
command (or crontab
) to schedule a swap cleanup (swapoff -a
).
It seems that after a day of inactivity the kernel believes the entire GUI is no longer needed and wipes it from RAM (swaps it to disk).
The kernel is doing The Right Thing™ believing it. Why would it keep in RAM unused memory and so essentially waste it instead of using it as cache or something?
I don't think the Linux kernel is gratuitously or anticipatory swapping out pages so if it does it, that must be to store something else on RAM, thus improving performance.
If you know when you'll need to reuse your laptop in advance, you might use the at
command (or crontab
) to schedule a swap cleanup (swapoff -a
).
answered 12 hours ago
jlliagrejlliagre
47.1k784133
47.1k784133
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
add a comment |
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
1
1
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
Thanks for the thought on possible causes. I've added a little to the question since it might be relevant. I wonder if there's a way to lower the priority of caching against application's own memory.
– Philip Couling
11 hours ago
add a comment |
Here's an idea, which I haven't tried myself (and I'm sorry I haven't the time right now to experiment with this).
Suppose you create a small VM with only 512MB memory for your background process I'm not sure if you'd want this to have any swap, your call, and switch off swap on your host system.
add a comment |
Here's an idea, which I haven't tried myself (and I'm sorry I haven't the time right now to experiment with this).
Suppose you create a small VM with only 512MB memory for your background process I'm not sure if you'd want this to have any swap, your call, and switch off swap on your host system.
add a comment |
Here's an idea, which I haven't tried myself (and I'm sorry I haven't the time right now to experiment with this).
Suppose you create a small VM with only 512MB memory for your background process I'm not sure if you'd want this to have any swap, your call, and switch off swap on your host system.
Here's an idea, which I haven't tried myself (and I'm sorry I haven't the time right now to experiment with this).
Suppose you create a small VM with only 512MB memory for your background process I'm not sure if you'd want this to have any swap, your call, and switch off swap on your host system.
answered 12 hours ago
X TianX Tian
7,66712136
7,66712136
add a comment |
add a comment |
Is the process you're running something you've created yourself?
If so, it might be worth tweaking your code to open the files using the O_DIRECT
flag, which to quote the manual page -
Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT. See NOTES below for further discussion.
add a comment |
Is the process you're running something you've created yourself?
If so, it might be worth tweaking your code to open the files using the O_DIRECT
flag, which to quote the manual page -
Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT. See NOTES below for further discussion.
add a comment |
Is the process you're running something you've created yourself?
If so, it might be worth tweaking your code to open the files using the O_DIRECT
flag, which to quote the manual page -
Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT. See NOTES below for further discussion.
Is the process you're running something you've created yourself?
If so, it might be worth tweaking your code to open the files using the O_DIRECT
flag, which to quote the manual page -
Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT. See NOTES below for further discussion.
answered 8 hours ago
Will CrawfordWill Crawford
21014
21014
add a comment |
add a comment |
Remove swap or diminish it about 20% (may vary with systems) as recently OS are not using swap anymore the same way as they did in the few years ago. It probably answer some of your question:
here --> official redhat.com
important info:
In the past, some application vendors recommended swap of a size equal to
the RAM, or even twice the RAM. Now let us imagine the above-mentioned
system with 2GB of RAM and 2GB of swap. A database on the system was by
mistake configured for a system with 5GB of RAM. Once the physical memory is
used up, swap gets used. As the swap disk is much slower than RAM, the
performance goes down, and thrashing occurs. At this point, even logins into
the system might become impossible. As more and more memory gets written to,
eventually both physical- and swap memory are completely exhausted and the
OOM killer kicks in, killing one or more processes. In our case, quite a lot
of swap is available, so the time of poor performance is long.
and
https://wiki.debian.org/Swap
small portion of link above:
Information and considerations related to the amount of swap to use:
"The recommended amount of swap space has traditionally been double the amount of
system memory. This has changed over time to one and half times system memory, both
answers are decent baselines but are becoming less and less useful answers to the
question as time passes. There are many variables about your system and intended use
that will determine the available system swap you will want to have."
You may try:
Best way to disable swap in linux
Personal note:
Since I've 6GB RAM and in all my recently Linux OS. I've never ever seem any indication of use of Swap. I determined it I must turn it off either for space (few gigs more) and because it has slowered my system sometimes.
New contributor
add a comment |
Remove swap or diminish it about 20% (may vary with systems) as recently OS are not using swap anymore the same way as they did in the few years ago. It probably answer some of your question:
here --> official redhat.com
important info:
In the past, some application vendors recommended swap of a size equal to
the RAM, or even twice the RAM. Now let us imagine the above-mentioned
system with 2GB of RAM and 2GB of swap. A database on the system was by
mistake configured for a system with 5GB of RAM. Once the physical memory is
used up, swap gets used. As the swap disk is much slower than RAM, the
performance goes down, and thrashing occurs. At this point, even logins into
the system might become impossible. As more and more memory gets written to,
eventually both physical- and swap memory are completely exhausted and the
OOM killer kicks in, killing one or more processes. In our case, quite a lot
of swap is available, so the time of poor performance is long.
and
https://wiki.debian.org/Swap
small portion of link above:
Information and considerations related to the amount of swap to use:
"The recommended amount of swap space has traditionally been double the amount of
system memory. This has changed over time to one and half times system memory, both
answers are decent baselines but are becoming less and less useful answers to the
question as time passes. There are many variables about your system and intended use
that will determine the available system swap you will want to have."
You may try:
Best way to disable swap in linux
Personal note:
Since I've 6GB RAM and in all my recently Linux OS. I've never ever seem any indication of use of Swap. I determined it I must turn it off either for space (few gigs more) and because it has slowered my system sometimes.
New contributor
add a comment |
Remove swap or diminish it about 20% (may vary with systems) as recently OS are not using swap anymore the same way as they did in the few years ago. It probably answer some of your question:
here --> official redhat.com
important info:
In the past, some application vendors recommended swap of a size equal to
the RAM, or even twice the RAM. Now let us imagine the above-mentioned
system with 2GB of RAM and 2GB of swap. A database on the system was by
mistake configured for a system with 5GB of RAM. Once the physical memory is
used up, swap gets used. As the swap disk is much slower than RAM, the
performance goes down, and thrashing occurs. At this point, even logins into
the system might become impossible. As more and more memory gets written to,
eventually both physical- and swap memory are completely exhausted and the
OOM killer kicks in, killing one or more processes. In our case, quite a lot
of swap is available, so the time of poor performance is long.
and
https://wiki.debian.org/Swap
small portion of link above:
Information and considerations related to the amount of swap to use:
"The recommended amount of swap space has traditionally been double the amount of
system memory. This has changed over time to one and half times system memory, both
answers are decent baselines but are becoming less and less useful answers to the
question as time passes. There are many variables about your system and intended use
that will determine the available system swap you will want to have."
You may try:
Best way to disable swap in linux
Personal note:
Since I've 6GB RAM and in all my recently Linux OS. I've never ever seem any indication of use of Swap. I determined it I must turn it off either for space (few gigs more) and because it has slowered my system sometimes.
New contributor
Remove swap or diminish it about 20% (may vary with systems) as recently OS are not using swap anymore the same way as they did in the few years ago. It probably answer some of your question:
here --> official redhat.com
important info:
In the past, some application vendors recommended swap of a size equal to
the RAM, or even twice the RAM. Now let us imagine the above-mentioned
system with 2GB of RAM and 2GB of swap. A database on the system was by
mistake configured for a system with 5GB of RAM. Once the physical memory is
used up, swap gets used. As the swap disk is much slower than RAM, the
performance goes down, and thrashing occurs. At this point, even logins into
the system might become impossible. As more and more memory gets written to,
eventually both physical- and swap memory are completely exhausted and the
OOM killer kicks in, killing one or more processes. In our case, quite a lot
of swap is available, so the time of poor performance is long.
and
https://wiki.debian.org/Swap
small portion of link above:
Information and considerations related to the amount of swap to use:
"The recommended amount of swap space has traditionally been double the amount of
system memory. This has changed over time to one and half times system memory, both
answers are decent baselines but are becoming less and less useful answers to the
question as time passes. There are many variables about your system and intended use
that will determine the available system swap you will want to have."
You may try:
Best way to disable swap in linux
Personal note:
Since I've 6GB RAM and in all my recently Linux OS. I've never ever seem any indication of use of Swap. I determined it I must turn it off either for space (few gigs more) and because it has slowered my system sometimes.
New contributor
edited 11 hours ago
New contributor
answered 11 hours ago
Tyþë-ØTyþë-Ø
343
343
New contributor
New contributor
add a comment |
add a comment |
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6
Define "emergency" and say something about how this is different from any ordinary situation when swap would be used.
– Kusalananda
13 hours ago
1
I wanted to know if you wanted to somehow define a special type of out-of-bounds "emergency event" that would allow the kernel to use swap, but that swap would otherwise not be used. AFAIK paging out memory is something that is slow and only ever done "in emergencies" anyway, and the "swappiness" thing is the only thing that you are able use to adjust this behaviour with (but I'm no Linux user).
– Kusalananda
12 hours ago
1
No that's not correct. It's not only done in emergencies. At the very least I thought my question made it clear I've only used 3GB out of 8GB... That's hardly an emergency but the kernel is swapping anyway. I suggest you read up on swappiness and surrounding topics. There is quite a bit of discussion over the various reasons for swapping. It is plausible I'm asking for a concept that doesn't exist in the kernel, but my reasons for asking for it are reasonably well justified..
– Philip Couling
12 hours ago
1
Here's another discussion on the same subject, I noticed this issue about 19 years ago and still haven't seen a solution, but unfortunately receive a few sarcastic comments anytime I brought it up.
– X Tian
12 hours ago
1
I recognise the advice always has been "never run without swap". But memory sizes have out scaled hard drive (HDD not SSD) read/write speeds meaning that swap is increasingly a bad idea. It feels like some believe 8GB RAM + 8GB swap will out perform 16GB RAM + 0 swap. If it truly does then something is very wrong with the Linux kernel.
– Philip Couling
12 hours ago