swap_cache_alloc_folio(9)

📦 version 7.3.1, in nixpkgs unstable

💅 swap_cache_alloc_folio — the kernel API manual, but make it cute

okay so bestie, welcome to section 9 of the Kernel API Manual, and today's main character is swap_cache_alloc_folio 🎀

✨ NAME ✨

swap_cache_alloc_folio — literally allocating a folio for a swapped-out slot in the swap cache 🦋

🌸 SYNOPSIS 🌸

struct folio * swap_cache_alloc_folio (swp_entry_t targ_entry , gfp_t
gfp , unsigned long orders , struct vm_fault *vmf , struct mempolicy
*mpol , pgoff_t ilx );

like, six arguments, no cap. she's high maintenance but she's worth it 💅

🫶 ARGUMENTS 🫶

  • targ_entry — the swap entry that points at the target slot. this is the one you're shopping for ✨
  • gfp — the memory allocation flags. the vibe settings for how we allocate, basically.
  • orders — the allocation orders. must be non-zero, fr fr, zero is not it 🙈
  • vmf — the fault information. all the deets about the fault that brought us here.
  • mpol — the NUMA memory allocation policy to be applied. yes we're being picky about where the memory lives 👑
  • ilx — the NUMA interleave index. only for use when it's MPOL_INTERLEAVE, iykyk.

💖 DESCRIPTION 💖

so what she does: she allocates a folio in the swap cache for one swap slot. typically this happens before doing IO — think swap in, or zswap writeback 🌈

the swap slot that targ_entry points at must have a non-zero swap count, meaning it's actually swapped out. that's the vibe check it has to pass ✋

🔥 CONTEXT 🔥

the caller has to protect the swap device — either with a reference count or with locks. no freelancing, bestie, protect your device 😤

⭐ RETURN ⭐

  • she returns the folio if the allocation succeeded and the folio is chillin' in the swap cache 🎀
  • she returns an error code if it failed — because of a race, OOM, or invalid arguments. and yes, invalid arguments is a real one, so mind your orders 💀

🦋 SEE ALSO 🦋

kernel file ./mm/swap_state.c and honestly the whole friend group:

like, the entire swap cache friend group showed up to the group chat 😭💜

and that's the page!! sourced from ./mm, dated October 2026 — mwah, go read your swap cache code bestie, slay 🧚‍♀️🍓💫

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