# Shared memory performance

**URL:** <https://forums.docker.com/t/shared-memory-performance/127684>\
**Category:** General\
**Created:** [August 10, 2022, 2:58pm UTC](https://forums.docker.com/t/shared-memory-performance/127684 "2022-08-10T14:58:41Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![somedudeontheinternet](https://avatars.discourse-cdn.com/v4/letter/s/90ced4/32.png) [@somedudeontheinternet](https://forums.docker.com/u/somedudeontheinternet)\
**Post date:** [August 10, 2022, 2:58pm UTC](https://forums.docker.com/t/shared-memory-performance/127684/1 "2022-08-10T14:58:41Z")

</div>

Hi,  
I have been doing some benchmarking and noticed that shared memory is always a bit slower if run in a container.  
I have got two processes which share a memory region, created with `shm_open()` and mapped with `mmap()`.  
The first process generates some random message and writes it into the shared memory region and the second process which runs in a container (using the hosts ipc namespace) copies this message into its own virtual address space.  
I noticed that is takes just a little longer transmitting the message (this includes writing the message into the shared memory and copping it into to second processes address space), compared to running both parts as a plain old process. I ran the benchmark with a message size of 32, 1024, 2048, 4096 and 9812 Bytes each 5000 times. It takes between 25 and 60% longer (linearly growing with the message size) when the second part is run in a container.  
_So my question is_: where does this overhead get introduced? Is some technique comparable to KSM (Kernel Samepage Merging) used probably not right?  
I hope that question is not to trivial but I have a very limited understanding of cgroups, namespaces etc. so I thought I’d just ask you guys and girls because I didn’t really find anything regarding the shmem performance on docker.

Thanks a lot for even reading this.