cpuset_spread_node(9)

📦 version 7.3.1, in nixpkgs unstable

💅 cpuset_spread_node(9) — like, the Kernel API Manual, but make it make sense

okay bestie, welcome to the cpuset_spread_node(9) page ✨ this is the whole kernel-API-manual moment, and no cap, it's a short one, so we're gonna absolutely devour it.

🌸 NAME 🌸

cpuset_spread_node — literally just answers the question: on which node do we begin search for a page? 🎀

✨ SYNOPSIS ✨

int cpuset_spread_node (int *rotor );

that's it. that's the whole call. iconic.

🦋 ARGUMENTS 🦋

  • rotor — the round robin rotor 💫 yes it's called a rotor, yes that's a real word here, we love a spinning-adjacent naming moment.

🔥 DESCRIPTION 🔥

okay so here's the vibe 👑 when a task is marked PFA_SPREAD_PAGE and a page cache allocation uses cpuset_mem_spread_node to figure out where to start looking, this routine spreads that starting node around the task's mems_allowed nodes instead of just starting on the local node. spreading the love, spreading the search 💖

and ngl, we don't have to worry about the returned node being offline, because "it can't happen" 😭 (yes, that's the actual reasoning, and honestly? mood). and even if it did happen, it would be okay. no drama.

here's why: the routines calling guarantee_online_mems are careful to only set nodes in task->mems_allowed that are online 🫶 so like, it should genuinely not be possible for the following code to return an offline node. but if it did, that would still be okay — because this routine is not returning the node where the allocation must be, only the node where the search should start. the zonelist the allocator uses will include all nodes ⭐ and if the slab allocator gets passed an offline node, it'll fall back to the local node. see kmem_cache_alloc_node for that whole situation 💀

bestie reminder: "it can't happen" is doing a lot of emotional labour in this paragraph, so keep the fallback behaviour in mind. this is a hint, not a promise 💅

💜 SEE ALSO 💜

kernel file ./kernel/cgroup/cpuset.c, plus the whole friend group:

aaaand that's the page 🎀 this whole thing lives under ./kernel/cgroup — that's the source — and the version/date stamp on it is October 2026, so mark your calendar bestie 🗓️✨ slay, go read the cpuset source, ily, bye 💖

📦 where this page comes from