register_mt...ce_algorithm(9)

💅 register_mt_adistance_algorithm(9) — the kernel API manual, but make it make sense

okay so bestie, welcome to the Kernel API Manual page for register_mt_adistance_algorithm ✨ this is the one you go to when you've written a memory tiering abstract distance algorithm and you need the kernel to ~actually know about it~ 🎀

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✨ NAME ✨

register_mt_adistance_algorithm — register a memory tiering abstract distance algorithm 🦋

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🌸 SYNOPSIS 🌸

int register_mt_adistance_algorithm (struct notifier_block *nb );

that's it, that's the whole vibe check 💅

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🫶 ARGUMENTS 🫶

• nb — the notifier block that describes your algorithm. it's giving "here's my whole personality, kernel" 🙈

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⭐ RETURN ⭐

• 0 on success 🌈
• errno on error 💀

no in-between, no "it depends", periodt ✨

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👑 DESCRIPTION 👑

so every memory tiering abstract distance algorithm provider needs to register its algorithm with register_mt_adistance_algorithm — like, that's the whole ritual, no cap 🕯️

when the kernel needs to calculate the abstract distance for a specified memory node, your notifier function gets called — unless some high priority algorithm has already provided a result (in which case, respectfully, you don't get the aux 😭).

the prototype of the notifier function is literally this:

int (*algorithm_notifier)(struct notifier_block *nb, unsigned long nid, void *data);

where:

• nid specifies the memory node 🧚
• data is the pointer to the returned abstract distance — that is, int *adist 🔥

here's the important bit, bestie, listen up: if your algorithm provides the result, you should return NOTIFY_STOP ✋ like, you're done, drop the mic, everyone else can go home 💅

otherwise, return return_value & NOTIFY_STOP_MASK == 0 so the next algorithm in the chain gets a chance to provide the result 🌸 iykyk

fr fr do not sleep on that mask check — it's literally the difference between "I got this" and "next bestie, you're up" 🫶

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🌈 SEE ALSO 🌈

• Kernel file ./mm/memory-tiers.c
• folio_use_access_time(9)
• next_demotion_node(9)
• unregister_mt_adistance_algorithm(9)
• mt_calc_adistance(9)

like, read them, they're all iconic in their own way 💖

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and that's the whole page, diva 🎀 this came out of ./mm with the October 2026 date attached, so go forth and register your algorithm — the kernel is literally waiting for your main character energy 👑✨💜