fadump_calc...reserve_size(9)

🌸 fadump_calculate_reserve_size — a.k.a. the "how much RAM do we gatekeep for boot" girlie ✨

ok bestie, welcome to the Kernel API Manual 💅 this one's about fadump_calculate_reserve_size, and yes that name is a mouthful, we're gonna get through it together 🫶

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✨ NAME ✨

fadump_calculate_reserve_size — reserve variable boot area 5% of System RAM 🎀

like, literally, that's her whole job. five percent. of your RAM. for boot. iconic behaviour tbh 👑

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🌈 SYNOPSIS 🌈

u64 fadump_calculate_reserve_size (void );

no cap, that's it. that's the whole call. 🦋

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💜 ARGUMENTS 💜

• void — no arguments. zero. zilch. she takes nothing, she gives everything 😭✨

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🔥 DESCRIPTION 🔥

okay so here's the vibe check 💀

This is the function that finds the largest memory size we need to reserve during the early boot process. and what does "largest memory size" even mean here? it means the size of the memory that's required for a kernel to boot successfully. that's the whole assignment. that's the mission 🎯

ngl, this function has been taken from the phyp-assisted dump feature</> implementation. so she's got history. she's a legacy icon. we respect her 🙇‍♀️

and what does she return? slay, glad you asked:

• returns the larger of 256MB or 5% rounded down to multiples of 256MB 💖

so it's giving "bigger of two things, one of which is all roundy and polite about multiples of 256MB." math girlie behaviour fr fr 🧮✨

⚠️ TODO: come up with a better approach to find out more accurate memory size that is required for a kernel to boot successfully. like, the devs literally left a note saying "yeah this could be better" and honestly? same energy as leaving a // TODO: fix later at 3am 😭💀

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🦋 SEE ALSO 🦋

• Kernel file ./arch/powerpc/kernel/fadump.c — go read the source bestie, it's all in there 📖💅

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and that's the page!! 🌸 this gem lives over in ./arch/powerpc/kernel, dated October 2026, and it's part of the fadump_calc...reserve_size(9) situation — go off, kernel girlie, reserve that boot memory 👑💖✨