__folio_split(9)

📦 version 7.3.1, in nixpkgs unstable

💅 __folio_split — the Kernel API Manual girlie is here to explain it ✨

okay so bestie, this is __folio_split(9) from the Kernel API Manual, and it's literally the function that splits a folio at @split_at down to a @new_order folio. icon behavior. let's get into it 🫶

🌸 SYNOPSIS 🌸

int __folio_split (struct folio *folio , unsigned int new_order , struct
page *split_at , struct page *lock_at , struct list_head *list , enum
split_type split_type );

🎀 ARGUMENTS 🎀

  • folio — the folio you're splitting, bestie. that's the main character 💅
  • new_order — the order of the new folio (yes it's an unsigned int, no we're not debating it)
  • split_at — a page within the new folio 📍
  • lock_at — a page within folio that gets left locked for the caller 🔒
  • list — after-split folios get put on it, but only if it's non-NULL 🧺
  • split_type — tells it whether to do a uniform split or not (not uniform = the non-uniform split) 🌈

✨ DESCRIPTION ✨

So it calls __split_unmapped_folio to actually perform the uniform and non-uniform split. it's also the one in charge of checking whether the split is even supported or not, and of preparing the folio for __split_unmapped_folio. basically it's the responsible friend of the group chat 🫡

After splitting, the after-split folio containing lock_at stays locked, and all the others get unlocked. and that looks like:

  1. for uniform split, lock_at points to one of folio's subpages 👑
  2. for buddy allocator like (non-uniform) split, lock_at points to folio itself 💀

🔥 RETURN 🔥

  • 0 — successful, slay 💖
  • <0 — failed 😭 (and if -ENOMEM is returned, the folio might be split but not to new_order — so the caller needs to check, no cap, do not skip this)
⚠️ fr fr: that -ENOMEM case is giving "partial success but make it stressful" — the caller has to check. don't just assume.

🦋 SEE ALSO 🦋

Kernel file ./mm/huge_memory.c — plus these icons:

aaaand that's the page 💜 it lives in ./mm and the version/date stamp on this one is October 2026 — so future-core of it, honestly. mwah, go split some folios responsibly 👑🎀

📦 where this page comes from