i don’t believe it’s entirely related to pulseaudio, but pulseaudio is definitely a major contributing factor.
the memory pages take so much of the limited 32-bit address space that you run out of memory before you’re even playing on a majority of darkrps (and other large gamemodes) in 2017.
there are (probably) other contributing factors that windows just doesn’t deal with, but i don’t have time to stare at the memory maps gmod has while open and figure out what is causing them to be created, (it’s obviously not realistic to modify the game to use less memory) and we can really only hope to get the same memory usage the windows version has. (which, with making the pulseaudio pages smaller, we have basically achieved.)
on another note, pulseaudio is really bad, and someone should go on their ircs and tell them that. the amount of searching i had to do just to find out if that was an option (and, if i didn’t make it clear, the option is shm-size-bytes in /etc/pulse/client.conf and /etc/pulse/daemon.conf) was absurd. (not to mention that there was barely any explanation as to what pulseaudio would actually do when it has a smaller map of a memfd, which i still don’t have any knowledge of.)
[editline]19th October 2017[/editline]
while this isn’t wrong, it should be noted that higher video settings in gmod (specifically things like model detail[?] and texture detail, shader-oriented things should be negligible) have a definite impact on memory (the reason is somewhat obvious), you can test it by setting your video settings to the lowest possible, writing down the memory usage of the process (there’s only one that really matters), and setting texture detail to “very high”. your memory usage should jump up by ~250mb off of that alone.
gmod looks bad regardless, but note that the pulseaudio memory page size trick is of at least double the magnitude in impact.