Comment by jeffbee 5 days ago
I don't think that's really a position that can be defended. Both jemalloc and tcmalloc evolved and were refined in antagonistic multitenant environments without one overwhelming application. They are optimal for that exact thing.
It's possible that they were referring to something specific about their platform and its system allocator, but like I said it was an anecdote about one engineer's statement. I just remember thinking it sounded fair at the time.
The “system” allocator is managing memory within a process boundary. The kernel is responsible for managing it across processes. Claiming that a user space allocator is greedily inefficient is voodoo reasoning that suggests the person making the claim has a poor grasp of architecture.
There are shared resources involved though, for example one process can cause a lot of traffic in khugepaged. However I would point out that is an endemic risk of Linux's overall architecture. Any process can cause chaos by dirtying pages, or otherwise triggering reclaim.
That’s generally true of any allocator and assuming glibc’s behavior would help mitigate this is critically not something kernel engineers design around nor something glibc allocator is trying to achieve as a design goal.
For context, the "allocator engineer" I was talking to was a kernel engineer - they have an extremely solid grasp of their platform's architecture.
The whole advantage of being the platform's system allocator is that you can have a tighter relationship between the library function and the kernel implementation.
I’m not generally aware of any system allocator that’s written hand in glove with the kernel’s allocator or somehow interops better for overall system efficiency at the cost of behavior in-app. Care to provide an example?
> Both jemalloc and tcmalloc evolved and were refined in antagonistic multitenant environments without one overwhelming application. They are optimal for that exact thing.
They were mostly optimised on Facebook/Google server-side systems, which were likely one application per VM, no? (Unlike desktop usage where users want several applications to run cooperatively). Firefox is a different case but apparently mainline jemalloc never matched Firefox jemalloc, and even then it's entirely plausible that Firefox benefitted from a "selfish" allocator.