pcpu_block_update_hint_free(9)

📦 version 7.3.1, in nixpkgs unstable

💖 NAME 💖

Okay bestie, welcome to pcpu_block_update_hint_free(9) from the Kernel API Manual ✨ This one is literally called pcpu_block_update_hint_free — it updates the block hints on the free path 🫶

🌸 SYNOPSIS 🌸

void pcpu_block_update_hint_free (struct pcpu_chunk *chunk , int bit_off
, int bits );

🦋 ARGUMENTS 🦋

  • chunk — chunk of interest 👀 the one we're looking at
  • bit_off — chunk offset 📍
  • bits — size of request 🧮

💅 DESCRIPTION 💅

So what this icon actually does: it updates metadata for the allocation path. The whole point is that this avoids a blind block refresh by making use of the block contig hints — like, why blindly refresh when the hints are right there? 💁‍♀️ If that fails, it scans forward and backward to determine the extent of the free area. That scan is capped at the boundary of blocks, no cap beyond the block boundary periodt 💀

A chunk update is triggered if a page becomes free, a block becomes free, or the free spans across blocks. This tradeoff is to minimize iterating over the block metadata to update chunk_md->contig_hint. Heads up bestie: chunk_md->contig_hint may be off by up to a page, but it will never be more than the available space. If the contig hint is contained in one block, it will be accurate 💯

No cap, but literally there is a cap: the free-area scan stops at the block boundary 🧚

🌈 SEE ALSO 🌈

Kernel file ./mm/percpu.c is the home base 🏠 and these are the besties listed in SEE ALSO:

Later bestie, mwah 💋 — source ./mm, dated October 2026 🎀✨

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