Maximum number of threads per process in Linux

Question

What is the maximum number of threads that can be created by a process under Linux   How  if possible  can this value be modified

User · Answer

Yes  to increase the threads number you need to increase the virtual memory or decrease the stack size  In Raspberry Pi I didn   t find a way to increase the virtual memory  if a decrease the stack size from default 8MB to 1MB It is possibly get more than 1000 threads per process but decrease the stack size with the    ulimit -s    command make this for all threads  So  my solution was use    pthread t    instance    thread class    because the pthread t let me set the stack size per each thread  Finally  I am available to archive more than 1000 threads per process in Raspberry Pi each one with 1MB of stack

User · Answer

In practical terms  the limit is usually determined by stack space  If each thread gets a 1MB stack  I can t remember if that is the default on Linux   then you a 32-bit system will run out of address space after 3000 threads  assuming that the last gb is reserved to the kernel    However  you ll most likely experience terrible performance if you use more than a few dozen threads  Sooner or later  you get too much context-switching overhead  too much overhead in the scheduler  and so on   Creating a large number of threads does little more than eat a lot of memory  But a lot of threads with actual work to do is going to slow you down as they re fighting for the available CPU time   What are you doing where this limit is even relevant

User · Answer

Linux doesn t have a separate threads per process limit  just a limit on the total number of processes on the system  threads are essentially just processes with a shared address space on Linux  which you can view like this   cat  proc sys kernel threads-max   The default is the number of memory pages 4   You can increase this like   echo 100000  gt   proc sys kernel threads-max   There is also a limit on the number of processes  and hence threads  that a single user may create  see ulimit getrlimit for details regarding these limits

User · Answer

check the stack size per thread with ulimit  in my case Redhat Linux 2 6        ulimit -a         stack size               kbytes  -s  10240   Each of your threads will get this amount of memory  10MB  assigned for it s stack  With a 32bit program and a maximum address space of 4GB  that is a maximum of only 4096MB   10MB   409 threads     Minus program code  minus heap-space will probably lead to an observed max  of 300 threads    You should be able to raise this by compiling and running on 64bit or setting ulimit -s 8192 or even ulimit -s 4096  But if this is advisable is another discussion

User · Answer

In practical terms  the limit is usually determined by stack space  If each thread gets a 1MB stack  I can t remember if that is the default on Linux   then you a 32-bit system will run out of address space after 3000 threads  assuming that the last gb is reserved to the kernel    However  you ll most likely experience terrible performance if you use more than a few dozen threads  Sooner or later  you get too much context-switching overhead  too much overhead in the scheduler  and so on   Creating a large number of threads does little more than eat a lot of memory  But a lot of threads with actual work to do is going to slow you down as they re fighting for the available CPU time   What are you doing where this limit is even relevant

User · Answer

It probably shouldn t matter   You are going to get much better performance designing your algorithm to use a fixed number of threads  eg  4 or 8 if you have 4 or 8 processors    You can do this with work queues  asynchronous IO  or something like libevent

User · Answer

check the stack size per thread with ulimit  in my case Redhat Linux 2 6        ulimit -a         stack size               kbytes  -s  10240   Each of your threads will get this amount of memory  10MB  assigned for it s stack  With a 32bit program and a maximum address space of 4GB  that is a maximum of only 4096MB   10MB   409 threads     Minus program code  minus heap-space will probably lead to an observed max  of 300 threads    You should be able to raise this by compiling and running on 64bit or setting ulimit -s 8192 or even ulimit -s 4096  But if this is advisable is another discussion

User · Answer

You can see the current value by the following command- cat  proc sys kernel threads-max  You can also set the value like  echo 100500    proc sys kernel threads-max  The value you set would be checked against the available RAM pages  If the thread structures occupies more than 1 8th  of the available RAM pages  thread-max would be reduced accordingly

User · Answer

In practical terms  the limit is usually determined by stack space  If each thread gets a 1MB stack  I can t remember if that is the default on Linux   then you a 32-bit system will run out of address space after 3000 threads  assuming that the last gb is reserved to the kernel    However  you ll most likely experience terrible performance if you use more than a few dozen threads  Sooner or later  you get too much context-switching overhead  too much overhead in the scheduler  and so on   Creating a large number of threads does little more than eat a lot of memory  But a lot of threads with actual work to do is going to slow you down as they re fighting for the available CPU time   What are you doing where this limit is even relevant

User · Answer

To set permanently    vim  etc sysctl conf   and add  kernel threads-max    value

User · Answer

Linux doesn t have a separate threads per process limit  just a limit on the total number of processes on the system  threads are essentially just processes with a shared address space on Linux  which you can view like this   cat  proc sys kernel threads-max   The default is the number of memory pages 4   You can increase this like   echo 100000  gt   proc sys kernel threads-max   There is also a limit on the number of processes  and hence threads  that a single user may create  see ulimit getrlimit for details regarding these limits

User · Answer

dragosrsupercool  Linux doesn t use the virtual memory to calculate the maximum of thread  but the physical ram installed on the system   max threads   totalram pages    8   8192   4096     http   kavassalis com 2011 03 linux-and-the-maximum-number-of-processes-threads     kernel fork c     The default maximum number of threads is set to a safe    value  the thread structures can take up at most half    of memory      max threads   mempages    8   THREAD SIZE   PAGE SIZE     So thread max is different between every system  because the ram installed can be from different sizes  I know Linux doesn t need to increase the virtual memory  because on 32 bit we got 3 GB for user space and 1 GB for the kernel  on 64 bit we got 128 TB of virtual memory  that happen on Solaris  if you want increase the virtual memory you need to add swap space

User · Answer

We can see the maximum number of threads defined in the following file in linux  cat  proc sys kernel threads-max   OR   sysctl -a   grep threads-max

User · Answer

proper 100k threads on linux   ulimit -s  256 ulimit -i  120000 echo 120000  gt   proc sys kernel threads-max echo 600000  gt   proc sys vm max map count echo 200000  gt   proc sys kernel pid max      100k-pthread-create-app   2018 update from  Thomas  on systemd systems    etc systemd logind conf  UserTasksMax 100000

User · Answer

Thread count limit     cat  proc sys kernel threads-max    How it is calculated   max threads   mempages    8   THREAD SIZE   PAGE SIZE     and  x86 64 page size  PAGE SIZE  is 4K  Like all other architectures  x86 64 has a kernel stack for every active thread  These thread stacks are THREAD SIZE  2 PAGE SIZE  big   for mempages    cat  proc zoneinfo   grep spanned   awk   totalpages totalpages  2  END  print totalpages      so actually the number is not related with limitation of thread memory stack size  ulimit -s    P S  thread memory stack limitation is 10M in my rhel VM  and for 1 5G memory  this VM can only afford 150 threads

User · Answer

Depends on your system  just write a sample program   by creating processes in a loop   and check using ps axo pid ppid rss vsz nlwp cmd  When it can no more create threads check  nlwp count   nlwp is the number threads   voila you got your fool proof answer instead of going thru books

User · Answer

proper 100k threads on linux   ulimit -s  256 ulimit -i  120000 echo 120000  gt   proc sys kernel threads-max echo 600000  gt   proc sys vm max map count echo 200000  gt   proc sys kernel pid max      100k-pthread-create-app   2018 update from  Thomas  on systemd systems    etc systemd logind conf  UserTasksMax 100000

User · Answer

We can see the maximum number of threads defined in the following file in linux  cat  proc sys kernel threads-max   OR   sysctl -a   grep threads-max

User · Answer

To retrieve it  cat  proc sys kernel threads-max  To set it  echo 123456789   sudo tee -a  proc sys kernel threads-max  123456789     of threads

User · Answer

It probably shouldn t matter   You are going to get much better performance designing your algorithm to use a fixed number of threads  eg  4 or 8 if you have 4 or 8 processors    You can do this with work queues  asynchronous IO  or something like libevent

User · Answer

This is WRONG to say that LINUX doesn t have a separate threads per process limit       Linux implements max number of threads per process indirectly     number of threads   total virtual memory    stack size 1024 1024    Thus  the number of threads per process can be increased by increasing total virtual memory or by decreasing stack size  But  decreasing stack size too much can lead to code failure due to stack overflow while max virtual memory is equals to the swap memory   Check you machine   Total Virtual Memory  ulimit -v  default is unlimited  thus you need to increase swap memory to increase this   Total Stack Size  ulimit -s  default is 8Mb   Command to increase these values   ulimit -s newvalue  ulimit -v newvalue    Replace new value with the value you want to put as limit   References   http   dustycodes wordpress com 2012 02 09 increasing-number-of-threads-per-process

User · Answer

Linux doesn t have a separate threads per process limit  just a limit on the total number of processes on the system  threads are essentially just processes with a shared address space on Linux  which you can view like this   cat  proc sys kernel threads-max   The default is the number of memory pages 4   You can increase this like   echo 100000  gt   proc sys kernel threads-max   There is also a limit on the number of processes  and hence threads  that a single user may create  see ulimit getrlimit for details regarding these limits

User · Answer

Thread count limit     cat  proc sys kernel threads-max    How it is calculated   max threads   mempages    8   THREAD SIZE   PAGE SIZE     and  x86 64 page size  PAGE SIZE  is 4K  Like all other architectures  x86 64 has a kernel stack for every active thread  These thread stacks are THREAD SIZE  2 PAGE SIZE  big   for mempages    cat  proc zoneinfo   grep spanned   awk   totalpages totalpages  2  END  print totalpages      so actually the number is not related with limitation of thread memory stack size  ulimit -s    P S  thread memory stack limitation is 10M in my rhel VM  and for 1 5G memory  this VM can only afford 150 threads

User · Answer

I think we missed another restriction which will also block the new thread creation  this is the kernel pid max limit  root myhost    lsb release -a No LSB modules are available  Distributor ID  Ubuntu Description     Ubuntu 16 04 7 LTS Release     16 04 Codename    xenial root myhost    uname -a Linux myhost 4 4 0-190-generic  220-Ubuntu SMP Fri Aug 28 23 02 15 UTC 2020 x86 64 x86 64 x86 64 GNU Linux  I find that at least in my system  this threshold kernel pid max is 32768  When I launch any simple JVM process  it reports error like below  java jstack jstat         There is insufficient memory for the Java Runtime Environment to continue    Cannot create GC thread  Out of system resources    An error report file with more information is saved as     root hs err pid1390 log  Check the memory  sufficient  root lascorehadoop-15a32    free -mh               total        used        free      shared  buff cache   available Mem            125G         11G         41G        1 2G         72G        111G Swap             0B          0B          0B  Check the system thread     ps -eLf wc -l 31506  But I check the system limit by ulimit  root myhost    ulimit -a core file size           blocks  -c  0 data seg size            kbytes  -d  unlimited scheduling priority              -e  0 file size                blocks  -f  unlimited pending signals                  -i  515471 max locked memory        kbytes  -l  64 max memory size          kbytes  -m  unlimited open files                       -n  98000 pipe size             512 bytes  -p  8 POSIX message queues      bytes  -q  819200 real-time priority               -r  0 stack size               kbytes  -s  8192 cpu time                seconds  -t  unlimited max user processes               -u  515471 virtual memory           kbytes  -v  unlimited file locks                       -x  unlimited  From the ulimit output  we could see that currently thread number is far less than the maximum user process limit  In fact  the limit which is reached is the kernel pid max Very easy to check and tuning it  https   www cyberciti biz tips howto-linux-increase-pid-limits html

User · Answer

This is WRONG to say that LINUX doesn t have a separate threads per process limit       Linux implements max number of threads per process indirectly     number of threads   total virtual memory    stack size 1024 1024    Thus  the number of threads per process can be increased by increasing total virtual memory or by decreasing stack size  But  decreasing stack size too much can lead to code failure due to stack overflow while max virtual memory is equals to the swap memory   Check you machine   Total Virtual Memory  ulimit -v  default is unlimited  thus you need to increase swap memory to increase this   Total Stack Size  ulimit -s  default is 8Mb   Command to increase these values   ulimit -s newvalue  ulimit -v newvalue    Replace new value with the value you want to put as limit   References   http   dustycodes wordpress com 2012 02 09 increasing-number-of-threads-per-process

User · Answer

It probably shouldn t matter   You are going to get much better performance designing your algorithm to use a fixed number of threads  eg  4 or 8 if you have 4 or 8 processors    You can do this with work queues  asynchronous IO  or something like libevent

User · Answer

Use nbio non-blocking i o library or whatever  if you need more threads for doing I O calls that block

User · Answer

You can see the current value by the following command- cat  proc sys kernel threads-max  You can also set the value like  echo 100500    proc sys kernel threads-max  The value you set would be checked against the available RAM pages  If the thread structures occupies more than 1 8th  of the available RAM pages  thread-max would be reduced accordingly

User · Answer

To retrieve it  cat  proc sys kernel threads-max  To set it  echo 123456789   sudo tee -a  proc sys kernel threads-max  123456789     of threads

User · Answer

To retrieve it  cat  proc sys kernel threads-max  To set it  echo 123456789   sudo tee -a  proc sys kernel threads-max  123456789     of threads

User · Answer

In practical terms  the limit is usually determined by stack space  If each thread gets a 1MB stack  I can t remember if that is the default on Linux   then you a 32-bit system will run out of address space after 3000 threads  assuming that the last gb is reserved to the kernel    However  you ll most likely experience terrible performance if you use more than a few dozen threads  Sooner or later  you get too much context-switching overhead  too much overhead in the scheduler  and so on   Creating a large number of threads does little more than eat a lot of memory  But a lot of threads with actual work to do is going to slow you down as they re fighting for the available CPU time   What are you doing where this limit is even relevant

User · Answer

It probably shouldn t matter   You are going to get much better performance designing your algorithm to use a fixed number of threads  eg  4 or 8 if you have 4 or 8 processors    You can do this with work queues  asynchronous IO  or something like libevent

User · Answer

For anyone looking at this now  on systemd systems  in my case  specifically Ubuntu 16 04  there is another limit enforced by the cgroup pids max parameter   This is set to 12 288 by default  and can be overriden in  etc systemd logind conf  Other advice still applies including pids max  threads-max  max maps count  ulimits  etc

User · Answer

Depends on your system  just write a sample program   by creating processes in a loop   and check using ps axo pid ppid rss vsz nlwp cmd  When it can no more create threads check  nlwp count   nlwp is the number threads   voila you got your fool proof answer instead of going thru books

User · Answer

For anyone looking at this now  on systemd systems  in my case  specifically Ubuntu 16 04  there is another limit enforced by the cgroup pids max parameter   This is set to 12 288 by default  and can be overriden in  etc systemd logind conf  Other advice still applies including pids max  threads-max  max maps count  ulimits  etc

User · Answer

To set permanently    vim  etc sysctl conf   and add  kernel threads-max    value

User · Answer

dragosrsupercool  Linux doesn t use the virtual memory to calculate the maximum of thread  but the physical ram installed on the system   max threads   totalram pages    8   8192   4096     http   kavassalis com 2011 03 linux-and-the-maximum-number-of-processes-threads     kernel fork c     The default maximum number of threads is set to a safe    value  the thread structures can take up at most half    of memory      max threads   mempages    8   THREAD SIZE   PAGE SIZE     So thread max is different between every system  because the ram installed can be from different sizes  I know Linux doesn t need to increase the virtual memory  because on 32 bit we got 3 GB for user space and 1 GB for the kernel  on 64 bit we got 128 TB of virtual memory  that happen on Solaris  if you want increase the virtual memory you need to add swap space

User · Answer

I think we missed another restriction which will also block the new thread creation  this is the kernel pid max limit  root myhost    lsb release -a No LSB modules are available  Distributor ID  Ubuntu Description     Ubuntu 16 04 7 LTS Release     16 04 Codename    xenial root myhost    uname -a Linux myhost 4 4 0-190-generic  220-Ubuntu SMP Fri Aug 28 23 02 15 UTC 2020 x86 64 x86 64 x86 64 GNU Linux  I find that at least in my system  this threshold kernel pid max is 32768  When I launch any simple JVM process  it reports error like below  java jstack jstat         There is insufficient memory for the Java Runtime Environment to continue    Cannot create GC thread  Out of system resources    An error report file with more information is saved as     root hs err pid1390 log  Check the memory  sufficient  root lascorehadoop-15a32    free -mh               total        used        free      shared  buff cache   available Mem            125G         11G         41G        1 2G         72G        111G Swap             0B          0B          0B  Check the system thread     ps -eLf wc -l 31506  But I check the system limit by ulimit  root myhost    ulimit -a core file size           blocks  -c  0 data seg size            kbytes  -d  unlimited scheduling priority              -e  0 file size                blocks  -f  unlimited pending signals                  -i  515471 max locked memory        kbytes  -l  64 max memory size          kbytes  -m  unlimited open files                       -n  98000 pipe size             512 bytes  -p  8 POSIX message queues      bytes  -q  819200 real-time priority               -r  0 stack size               kbytes  -s  8192 cpu time                seconds  -t  unlimited max user processes               -u  515471 virtual memory           kbytes  -v  unlimited file locks                       -x  unlimited  From the ulimit output  we could see that currently thread number is far less than the maximum user process limit  In fact  the limit which is reached is the kernel pid max Very easy to check and tuning it  https   www cyberciti biz tips howto-linux-increase-pid-limits html

User · Answer

To retrieve it  cat  proc sys kernel threads-max  To set it  echo 123456789   sudo tee -a  proc sys kernel threads-max  123456789     of threads

User · Answer

Use nbio non-blocking i o library or whatever  if you need more threads for doing I O calls that block

User · Answer

Yes  to increase the threads number you need to increase the virtual memory or decrease the stack size  In Raspberry Pi I didn   t find a way to increase the virtual memory  if a decrease the stack size from default 8MB to 1MB It is possibly get more than 1000 threads per process but decrease the stack size with the    ulimit -s    command make this for all threads  So  my solution was use    pthread t    instance    thread class    because the pthread t let me set the stack size per each thread  Finally  I am available to archive more than 1000 threads per process in Raspberry Pi each one with 1MB of stack

User · Answer

Linux doesn t have a separate threads per process limit  just a limit on the total number of processes on the system  threads are essentially just processes with a shared address space on Linux  which you can view like this   cat  proc sys kernel threads-max   The default is the number of memory pages 4   You can increase this like   echo 100000  gt   proc sys kernel threads-max   There is also a limit on the number of processes  and hence threads  that a single user may create  see ulimit getrlimit for details regarding these limits

[linux] Maximum number of threads per process in Linux?

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