Thanks Sean, What threw me was that VTune has one column Memory Allocated and another Memory Used. Both were ~200MB. Using htop I was able to verify what you said. Perhaps VTune needs to change their naming! -- Ryan McClue, Sydney ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Tuesday, October 5th, 2021 at 8:19 AM, Sean Greenslade <sean@xxxxxxxxxxxxxxxxxx> wrote: > On Sun, Oct 03, 2021 at 07:44:13AM +0000, Ryan McClue wrote: > > > I'm on an Ubuntu system and want to write to a PCM buffer and play it. > > > > I created the most basic C program that only calls pa_simple_new(). I > > > > launched this program into Intel VTune and performed a Memory > > > > Consumption analysis. It showed that libpulsecommon.so allocates > > > > ~200MB and pa_simple_new() allocates ~67MB. Why is so much memory > > > > allocated? > > Hi, Ryan. > > There are a few subtleties in Linux with regards to memory usage. First, > > I recommend taking a look at the usage through a tool like "top", and > > notice that it reports three separete values for memory usage: VIRT, > > RES, and SHR. These stand for Virtual, Resident, and Shared. Each of > > these behaves a little differently. > > VIRT is how many kilobytes of memory address space is currently used by > > the application. This includes all memory allocations, memory mapped > > files, libraries, and anything else that gets addressed by memory. But > > just because something is using memory address space doesn't necessarily > > mean that it's using physical memory. > > RES is how many kilobytes of physical memory are in use by > > the application. This is more or less the "true memory usage" of the > > application. > > The SHR number is how much shared memory is in use by the application. > > This can be things like libraries or shared buffers (which pulse uses to > > transfer audio data between processes). > > I ran a test of pacat-simple.c on my machine and got the following > > values: > > VIRT - 339 MB > > RES - 5.3 MB > > SHR - 4.6 MB > > So you can see that despite the fact that ~300 MB of address space is > > used, only ~5 MB of actual RAM is consumed, and most of that is shared > > memory (likely the libraries and IPC audio buffers). > > Also, something a little unintuitive about Linux and the way it > > allocates memory is that allocations don't actually get assigned to > > physical memory until they are used. If you call malloc(), you will get > > address space assigned which will add to your VIRT count but your RES > > count will stay the same. Once you insert values into those memory > > addresses, then the RES count will increase, but only by the amount you > > actually fill. This causes mallocs to be almost no cost memory-wise, > > and there's pretty much no harm in over-allocating memory if it's not > > used. > > In summary, don't worry about the VIRT memory consumed by a process; > > it's not the amount of physical RAM used. > > > Also, as pulseaudio is what is adopted by Ubuntu, is it > > > > true that I have no other choice than to use pulseaudio as it owns all > > > > the sound devices? > > This question would be better asked on an Ubuntu-specific list. That > > said, if your audio needs are very simple (e.g. only one application > > ever playing audio at a time), then it should be possible to disable > > pulseaudio and use ALSA directly. > > --Sean
