VM_FAULT_PREFAULT(9)

✨ VM_FAULT_PREFAULT(9) ✨

okay bestie, welcome to the Kernel Developer's Manual 💖 this one's a section 9 (kernel dev) page, and it's lowkey one of those little helpers that makes your whole system feel ✨smooth✨. let's get into it.

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🦋 NAME 🦋

vm_fault_prefault — cluster page faults into a process's address space

like, group them. bundle them. make them all happen together instead of one at a time. it's giving efficiency, fr fr. 👑

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🌸 SYNOPSIS 🌸

#include <sys/param.h>
#include <vm/vm.h>
#include <vm/pmap.h>

void
vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry);

it returns void, so no return value to obsess over. just vibes and side effects. 💅

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🎀 DESCRIPTION 🎀

The vm_fault_prefault() function provides a means of clustering pagefaults into a process's address space. clustering!! it's literally taking a bunch of would-be page faults and handling them as a group instead of making the CPU cry one fault at a time. 😭

It operates upon the physical map pmap. The entry argument specifies the entry to be prefaulted; the addra argument specifies the beginning of the mapping in the process's virtual address space. so: pmap is the physical map you're working on, entry is like "this is the thing, prefault it", and addra is where that mapping starts in the process's virtual address space. 🗺️✨

It is typically called by vm_fault() after the first page fault. so like, first fault happens, and then vm_fault() is like "aight bet, let's get the rest of these while we're here." 🫶

It benefits the execve(2) system call by eliminating repetitive calls to vm_fault(), which would otherwise be made to bring the process's executable pages into physical memory. basically, when you execve, you don't wanna be doing a million tiny vm_fault() calls one by one — this clusters them so the process's executable pages land in physical memory without all that repetitive drama. iconic behavior, no cap. 🔥

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🧚 IMPLEMENTATION NOTES 🧚

This is a machine-independent function which calls the machine-dependent pmap_is_prefaultable(9) helper function to determine if a page may be prefaulted into physical memory.

so real talk: the function itself is portable, but it has to ask the platform-specific pmap_is_prefaultable(9) "hey, can this page actually be prefaulted?" before it goes doing anything. it's giving "check with the locals first" and honestly? respect. 🙈

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💜 SEE ALSO 💜

• execve(2)
• pmap_is_prefaultable(9)

go read those too, bestie, they're the supporting cast. 🌈

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👑 AUTHORS 👑

This manual page was written by Bruce M Simpson <bms@spc.org>. absolute legend, we stan a manpage author. 🎀

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quick vibe check: this is a machine-independent function backed by a machine-dependent helper, it returns void, and it's your go-to for clustering page faults — especially around execve(2). don't forget it leans on pmap_is_prefaultable(9) before it prefaults anything. 💀✨

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and that's the whole page, bestie!! this one came from the Debian version of the manpage, dated July 21, 2003 — so yes it's an elder but it still ate and left no crumbs. 🍓🧚 stay clustered, stay slay, mwah 💖