mtrr_trim_uncached_memory(9)

okay bestie, welcome to mtrr_trim_uncached_memory(9) from the Kernel API Manual — it's literally the page about trimming RAM that MTRRs don't cover. no cap, it's giving kernel cleanup era. 💖

✨ NAME ✨

mtrr_trim_uncached_memory — trim RAM not covered by MTRRs 🎀

🦋 SYNOPSIS 🦋

int mtrr_trim_uncached_memory (unsigned long end_pfn );

🌸 ARGUMENTS 🌸

• end_pfn — the ending page frame number. that's the whole vibe, bestie. ✨

💅 DESCRIPTION 💅

okay so picture this: some buggy BIOSes don't setup the MTRRs properly for systems with certain memory configurations. iconic behavior, but make it stressful. 😭

This routine checks that the highest MTRR matches the end of memory. why? to make sure the MTRRs having a write back type cover all of the memory the kernel is intending to use. yes bestie, all of it. 👑

If that check doesn't line up, it'll trim any memory off the end by adjusting end_pfn, removing it from the kernel's allocation pools, and warning the user with an obnoxious message. not the obnoxious message 😭💀 but fr fr, that's what it does.

heads up: the buggy BIOSes part is doing a lot of work here — some BIOSes don't setup the MTRRs properly. no cap. 🫶

🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/kernel/cpu/mtrr/cleanup.c — go peek, iykyk. 🫶

source/version: ./arch/x86/kernel/cpu/mtrr · date: October 2026 · page: mtrr_trim_uncached_memory(9) — that's the footer, bestie, and it ate. periodt. 💅✨