STRUCT MM_MM_CID(9)

🌸 struct mm_mm_cid(9) 🌸

okay bestie, so this is straight out of the Kernel API Manual, section 9, and it's literally the storage situation for per-MM CID data 💅 like this struct is where all the CID bookkeeping for a whole mm lives, and you're gonna want to know every single field because they all matter, no cap.

✨ NAME ✨

struct mm_mm_cid — storage for per MM CID data 🎀

✨ SYNOPSIS ✨

struct mm_mm_cid {
    struct mm_cid_pcpu      __percpu *pcpu;
    unsigned int            mode;
    unsigned int            max_cids;
    struct irq_work         irq_work;
    struct work_struct      work;
    raw_spinlock_t lock;
    struct mutex            mutex;
    struct hlist_head       user_list;
    unsigned int            nr_cpus_allowed;
    unsigned int            users;
    unsigned int            pcpu_thrs;
    unsigned int            update_deferred;
 };

💖 Members 💖

• pcpu — the per-CPU storage for the CIDs that are associated to a CPU, iconic, we love per-CPU everything 🦋
• mode — tells you which mode we're in: it indicates per CPU mode and transition mode ✨
• max_cids — the exclusive maximum CID value, used for allocation and for convergence (yes, exclusive, note that 💀)
• irq_work — the irq_work that handles the affinity mode change case 🔥
• work — regular work that also handles the affinity mode change case, because sometimes you can't do it in irq context, iykyk
• lock — a spinlock protecting against affinity setting, which literally can't take a mutex 🙈
• mutex — a mutex to serialize forks and exits that are related to this mm
• user_list — the list of the MM CID users of a MM 🫶
• nr_cpus_allowed — the number of CPUs in the per-MM allowed CPUs map. heads up: the map is growth only 📈
• users — the number of tasks sharing this MM. this one is separate from mm::mm_users because that gets modified by mmget/mm_put from other entities that don't actually share the MM, so don't go confusing them bestie 😭
• pcpu_thrs — the threshold for switching back from per CPU mode ⭐
• update_deferred — a deferred switch back to per task mode is pending ⏳

🌈 SEE ALSO 🌈

Kernel file ./include/linux/rseq_types.h — plus struct rseq_event(9), struct rseq_ids(9), union rseq_slice_state(9), struct rseq_slice(9), struct rseq_data(9), struct sched_mm_cid(9), and struct mm_cid_pcpu(9) — go read them all, they're all connected fr fr 🧚

that's the whole vibe check, bestie — sourced from ./include/linux, dated October 2026, and officially titled struct mm_mm_cid(9). slay, you now know your CIDs 💜👑