I'm running a program which allocates 8mb stacks using mmap. While testing to see how many stacks I could allocate (aiming for 100,000), I see virtual memory size rise quickly as expected, and reserved size stay small (less than 1gb). The program then segfaults with Cannot allocate new fiber stack: Cannot allocate memory (Errno). Using gdb to rescue the segfault and then looking at htop, I have discovered this happens at around 256GB of virtual memory.
I've tried using prlimit --as=unlimited --rss=unlimited --memlock=unlimited --data=unlimited when running the program, but it doesn't seem to make a difference.
Is there a way to increase this limit? Is it advisable to increase this limit? Is there a better way for crystal to allocate stacks?
Maybe you're hitting the maximum of /proc/sys/vm/max_map_count. This setting sets a maximum on the number of mmaps your process can have. The default value is 65536. So it's likely not the size of memory you want to malloc, but the number of malloc calls that causes the error Cannot allocate memory.
You can try to increase the maximum with:
sysctl -w vm.max_map_count=131070
See also NPTL caps maximum threads at 65528?
I'd check your swap file size. if you are running out of swap then all those parameter changes wont help you until you fix that.
I'd recreate the failure and run free -h to see if there is any unused swap. If its all gone you will need to increase your swap size.
I have a Go Program and I want to run it on a switch. Since I cannot install Go on the switch itself, I just copy the executable and try to run. But I get the following error.
runtime: panic before malloc heap initialized
fatal error: runtime: cannot reserve arena virtual address space
runtime stack:
runtime.throw(0x8149b8b)
/usr/local/go/src/pkg/runtime/panic.c:520 +0x71
runtime.mallocinit()
/usr/local/go/src/pkg/runtime/malloc.goc:552 +0xf2
runtime.schedinit()
/usr/local/go/src/pkg/runtime/proc.c:150 +0x3a
_rt0_go()
/usr/local/go/src/pkg/runtime/asm_386.s:95 +0xf6`
How do I package the Go executable with all it's dependencies?
EDIT 1: Here is the ulimit -a dump.
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 40960
max locked memory (kbytes, -l) 32
max memory size (kbytes, -m) unlimited
open files (-n) 1024
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) 1024
virtual memory (kbytes, -v) 395067
file locks (-x) unlimited
TL;DR
Your Go app is not being able to allocate virtual memory to run. I've never developed for a switch before but if it's running linux or a unix variant, check group/user permissions and ulimit values to check if that user has any kind of restriction. Maybe this question might be of help
Longer version
So, your problem here is not go not being able to run without the go development environment because you really don't need it. Go is known for generating static binaries that by definition are self contained and don't depend on other libraries to run.
If you take a better look at your error message, you'll notice that it says:
"cannot reserve arena virtual address space"
You might be asking yourself "what is this arena?"
I quick look at malloc's source code gives us a hint:
Set up the allocation arena, a contiguous area of memory where
allocated data will be found. The arena begins with a bitmap large
enough to hold 4 bits per allocated word.
If you go through that source code you'll find your error message around here.
The runtime·SysReserve C function is the one that actually tries to reserve the virtual address space for the arena. If it can't allocate that, it will throw that error.
You can find code for the Linux implementation of it here.
As go normally tries to avoid big allocations as the might fail right away, if your user can't allocate something as small as 64K, it means your user has tight restrictions. As I have no idea which OS your switch is running and have no experience developing for them I can't go any further than this.
If you can provide more information, I can try to update this answer accordingly.
I'm trying to simulate memory exaustion. So here is what I'm thinking:
turn off over commiting.
reduce the available heap so that the memory exaustion can happen quicker.
Run the program under test.
My question is w.r.t 2: is there a trick that reduce the heap size that kernel will allocate? I can probably write another program that allocates a large amount of RAM but there might be a smarter way?
You can remove the maximum process memory size using the ulimit system call. The command is available from the shell. The option in question is the -v (max memory size), so for example to limit the process to a maximum of 2GB you would do:
ulimit -v 2097152
Then you launch the process from that shell.
If you use the -H option to ulimit, then it sets a hard limit which cannot be increased once it's set (root can increase the limit).
If you want control from a program, you can use the setrlimit system call, in a manner like:
#include <sys/types.h>
#include <sys/resource.h>
struct rlimit the_limit = { 2097152 * 1024, RLIM_INFINITY };
if (-1 == setrlimit(RLIMIT_AS, &the_limit)) {
perror("setrlimit failed");
}
This sets the soft limit to 2GB, you can set the hard limit by changing the RLIM_INFINITY value. Please note, you can only increase the hard limit if you're root.
This limit applies to the total amount of memory that can be used for the process, not just the memory that is usable as the heap.
The heap memory can be limited using the -d option. The equivalent name for the setrlimit call is RLIMIT_DATA. This limit applies to memory allocations only - e.g. malloc, mmap, static data.
If you use ulimit -d you can limit the data segment size, which is used for heap allocation (as well as global/static variables).
To simulate memory exhaustion, you can use also use mmap to map large memory segments and make sure that you "lock" them in memory. See the mmap man page on how to lock pages in memory. That way these will not get swapped, and the available memory will be reduced.
You may want to request several small sized segments (e.g. 256KB) if request for large contigious mmap segments fail. Moreoever if you want to go all the way, you may need to make your mmap process immune to the Linux "OOM killer" (by setting the OOM prio to -17). Else, when Linux sees that the system is running too low on free memory, it could select and kill your process which is calling the mmaps, in an attempt to free up memory.
experimenting with shm_open in linux and running into problems. i'm frequently resizing a shared memory segment with ftrunc and using mmap to remap the resized segment. however, right around the 20 megabyte mark i get ENOMEM from mmap.
things i have attempted to do to resolve the issue:
first, i found out about these sysctl parameters. i reconfigured them:
kernel.shmmax = 268435456
kernel.shmall = 2097152
(shmall is specified in pages)
the issue still occurred after this. investigating the details of the resize that causes the issue revealed that the call made to ftrunc to resize the shared memory object succeeded (the corresponding file in /dev/shm had the requested new size).
documentation from here http://pubs.opengroup.org/onlinepubs/009695399/functions/mmap.html suggests three possible causes for an ENOMEM errno:
[ENOMEM]
MAP_FIXED was specified, and the range [addr,addr+len) exceeds that allowed for the address space of a process; or, if MAP_FIXED was not specified and there is insufficient room in the address space to effect the mapping.
[ENOMEM]
[ML] [Option Start] The mapping could not be locked in memory, if required by mlockall(), because it would require more space than the system is able to supply. [Option End]
[ENOMEM]
[TYM] [Option Start] Not enough unallocated memory resources remain in the typed memory object designated by fildes to allocate len bytes. [Option End]
i am not using MAP_FIXED or locking, and the size of the image in /dev/shm suggests that the third reason is not the problem. my mmap call looks like this:
mmap(mem, length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)
where mem initially is 0 and thereafter refers to the last address mmap successfully mapped.
i found information suggesting that ulimit settings could be limiting the memory mappable into a single process, but i don't think the problem was here. just in case, ulimit -a looks like this on my machine:
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 20
file size (blocks, -f) unlimited
pending signals (-i) 16382
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 65536
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) unlimited
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
i hope this is an easy one :)
well, i found out what my problem was the other day. i misread the documentation for mmap, which says that mmap returns a mapping based on the first parameter (the previously mapped address in my case), and the result is defined by implementation. i took this as a suggestion that mmap might remap my previous mapping for me, but this was certainly not the case. this might only have been the case if i had used the MAP_FIXED flag, but i avoided this because the documentation recommended against it. in any case, it was necessary to use munmap to remove the previous mapping before creating a new one. i hope this post will help anyone making the same foolish misreading that i did
What is the maximum number of threads that can be created by a process under Linux?
How (if possible) can this value be modified?
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 > /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.
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/
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?
proper 100k threads on linux:
ulimit -s 256
ulimit -i 120000
echo 120000 > /proc/sys/kernel/threads-max
echo 600000 > /proc/sys/vm/max_map_count
echo 200000 > /proc/sys/kernel/pid_max
./100k-pthread-create-app
2018 update from #Thomas, on systemd systems:
/etc/systemd/logind.conf: UserTasksMax=100000
#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.
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
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?
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.
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...
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.
Use nbio
non-blocking i/o
library or whatever, if you need more threads for doing I/O calls that block
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
To set permanently,
vim /etc/sysctl.conf
and add
kernel.threads-max = "value"
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
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
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.
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.
If you using Suse, you need to use one of these methods
https://www.suse.com/support/kb/doc/?id=000015901
global,
/etc/systemd/system.conf
DefaultTasksMax=Value
For specific ssh service
/etc/systemd/system/sshd.service.d/override.conf
TasksMax=Value