CODEWITHSUNDEEP
linux-kernelbpfebpf
joz
joz

Reputation: 339

Why should userspace applications lock Ebpf maps?

When you create EBPF maps, memory is allocated in kernel space. And kernel memory never gets swapped out. Then, why is there a need for the userspace application to call setrlimit() with RLIMIT_MEMLOCK?

Upvotes: 2

Views: 496

Answers (1)

Qeole
Qeole

Reputation: 9134

RLIMIT_MEMLOCK refers to the amount of memory that may be locked into RAM, it is not specific to allocations in the user space memory address range. On pre-5.11 kernels, memory used for eBPF objects (programs, maps, BTF objects etc.) is accounted against this resource, meaning that if you create too many of them at a given time, or even in a short interval of time (given that there is a small delay after the deletion of an object before the kernel reclaims the corresponding memory area), you may hit the resource limit and get a -EPERM as an answer. For privileged users, calling setrlimit() to lift the restrictions on this resource is the usual workaround indeed.

Note that in Linux 5.11, rlimit-based accounting was dropped in favour of cgroup-based memory accounting. The rlimit had a number of downsides (refer to the cover letter linked above for details), and the cgroup-based accounting is more flexible, while allowing a better control and offering easier ways to retrieve the current amount of memory used. It should also reflect the actual memory consumption, while this was not necessarily the case with rlimit.

Upvotes: 4

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