io_uring_mlock_size(3)

💖 io_uring_mlock_size — get required memlock size for a ring 💖

okay bestie, so you know how io_uring is this whole liburing thing and you're like "how much memlock do I even need for my ring??" — this page is literally that. it's from the liburing manual, section 3 (that's the library-functions section, iykyk), and it's here to tell you the exact number so you don't have to guess. 🎀

✨ SYNOPSIS ✨

#include <liburing.h>

ssize_t io_uring_mlock_size(unsigned entries, unsigned flags);

🌸 DESCRIPTION 🌸

so io_uring_mlock_size(3) is the function that returns the required RLIMIT_MEMLOCK memory size for an io_uring ring that has entries entries and whatever setup flags you passed in. that's it, that's the whole job. 💅

now here's the tea, and it depends on your kernel:

• on newer kernels (5.12+), io_uring no longer requires any memlock memory, and this function will return 0. yes, zero, nothing, she's free 🦋
• on older kernels (5.11 and prior), this returns the required memory so that the caller can make sure there's enough RLIMIT_MEMLOCK space available before setting up a ring. like checking your bank balance before you tap your card, fr fr.

and if you want more control over the ring parameters? use io_uring_mlock_size_params(3) instead. that one's the glow-up version. ✨

🫶 RETURN VALUE 🫶

• returns the required memlock size in bytes on success 🌈
• returns 0 if no memlock is needed (hi, modern kernels) 👑
• or a negative errno value on error 😭

👀 SEE ALSO 👀

• io_uring_mlock_size_params(3)
• io_uring_memory_size(3)
• io_uring_queue_init(3)
• getrlimit(2)

lowkey important reminder: don't just vibe-check this number into existence — the whole point is calling it before you set up the ring, so future-you doesn't get yelled at by the kernel. 💀

and that's a wrap, bestie 💜 this was liburing-2.4, dated January 18, 2025 — mwah, go touch some ring buffers 🎀✨