Started: `memfile::hp`: `MFD_HUGETLB` can be used when a size is known to exceed into the boundary of a hugepage. Currently in the process of writing function to collect all possible hugepage sizes and generate the correct flag masks for `memfd_create(, MFD_HUGETLB | ...)` for each one; and the smallest one that contains the known size can be used for the `memfd_create()` call (if the size fits any at all.)

TODO: This will be a seperate comptime feature: `hugetlb`: Extend `memfile` with the ability to allocate apporpirately sized huge-pages when input size is known to extend into them.

Fortune for collect's current commit: Blessing − 吉

Cargo.lock

@@ -84,7 +84,7 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "collect"
-version = "1.0.1"
+version = "1.0.2"
 dependencies = [
  "bitflags",
  "bytes",

src/memfile.rs

@@ -16,6 +16,9 @@ use std::{
 pub mod fd;
 pub mod error;
 mod map;
+//TODO: #[cfg(feature="hugetlb")] 
+mod hp;
+
 
 /// Flags passed to `memfd_create()` when used in this module
 const MEMFD_CREATE_FLAGS: libc::c_uint = libc::MFD_CLOEXEC;

src/memfile/hp.rs

@@ -0,0 +1,35 @@
+//! # Huge pages
+//! Calculates available huge page sizes, and creates `memfd_create()` flag masks for a `MFD_HUGETLB` fd.
+use super::*;
+use std::{
+    path::Path,
+};
+use libc::{
+    MFD_HUGETLB,
+    MAP_HUGE_SHIFT,
+};
+
+/// The location in the kernel's API which shows all valid huge-page sizes.
+///
+/// This is a directory, and its subdirectories' *names* will contain the size in this format: `hugepages-(\d+)kB` (where the first capture-group is the size in kB.)
+/// The contents of those subdirectories themselves are irrelevent for our purpose.
+pub const HUGEPAGE_SIZES_LOCATION: &'static str = "/sys/kernel/mm/hugepages";
+
+/// Take a directory path and try to parse the hugepage size from it.
+///
+/// All subdirectories from `HUGEPAGE_SIZES_LOCATION` should be passed to this, and the correct system-valid hugepage size will be returned for that specific hugepage.
+fn find_size_bytes(path: impl AsRef<Path>) -> Option<usize>
+{
+    let path= path.as_ref();
+    if !path.is_dir() {
+	return None;
+    } 
+
+    let dir_name = path.file_name()?;
+    // location of the `-` in the dir name
+    let split_loc = memchr::memchr(b'-', dir_name.as_bytes())?;
+
+    //TODO: find the `k` (XXX: Is it always in kB? Or do we have to find the last non-digit byte instead?) For now, we can just memchr('k') I think -- look into kernel spec for this later.
+    
+    None
+}