linux-support 0.0.25

Comprehensive Linux support for namespaces, cgroups, processes, scheduling, parsing /proc, parsing /sys, signals, hyper threads, CPUS, NUMA nodes, unusual file descriptors, PCI devices and much, much more
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// This file is part of linux-support. It is subject to the license terms in the COPYRIGHT file found in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/linux-support/master/COPYRIGHT. No part of linux-support, including this file, may be copied, modified, propagated, or distributed except according to the terms contained in the COPYRIGHT file.
// Copyright © 2020 The developers of linux-support. See the COPYRIGHT file in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/linux-support/master/COPYRIGHT.


/// Transparent Huge Page (THP) defragmentation choice.
#[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
#[derive(Deserialize, Serialize)]
#[serde(deny_unknown_fields)]
pub enum TransparentHugePageDefragmentationChoice
{
	/// Never defragment.
	Never,

	/// Defer defragmentation until allocation requires it.
	Defer,

	/// Only for pages so specified by the `madvise()` (or `fadvise()`) syscall with the `MADV_HUGEPAGE` flag.
	Advise,

	/// Like `Defer` and `MAdvise`.
	///
	/// Only for pages so specified by the `madvise()` (or `fadvise()`) syscall with the `MADV_HUGEPAGE` flag.
	DeferAndAdvise,
}

impl Default for TransparentHugePageDefragmentationChoice
{
	#[inline(always)]
	fn default() -> Self
	{
		TransparentHugePageDefragmentationChoice::Never
	}
}

impl TransparentHugePageDefragmentationChoice
{
	#[inline(always)]
	fn to_value(self) -> (&'static [u8], bool)
	{
		use self::TransparentHugePageDefragmentationChoice::*;

		match self
		{
			Never => (b"never\n" as &[u8], false),
			Defer => (b"defer\n" as &[u8], true),
			Advise => (b"madvise\n" as &[u8], true),
			DeferAndAdvise => (b"defer+madvise\n" as &[u8], true),
		}
	}

	/// Changes defragmentation using the Kernel-internal `khugepaged` daemon thread for Transparent Huge Pages (THP).
	///
	/// * The kernel default for `pages_to_scan` is 4096.
	/// * The kernel default for `scan_sleep_in_milliseconds` is 10_000.
	/// * The kernel default for `alloc_sleep_millisecs` is 60_000.
	/// * The kernel default for `how_many_extra_small_pages_not_already_mapped_can_be_allocated_when_collapsing_small_pages` is 511. Also known as `max_ptes_none`. A higher value leads to use additional memory for programs. A lower value produces less gains in performance. The value itself has very little effect on CPU usage.
	/// * The kernel default for `how_many_extra_small_pages_not_already_mapped_can_be_swapped_when_collapsing_small_pages` is 64. Also known as `max_ptes_swap`. A higher value can cause excessive swap IO and waste memory. A lower value can prevent THPs from being collapsed, resulting in fewer pages being collapsed into THPs, and so lower memory access performance.
	///
	/// Can also be read as a value in `/sys/kernel/mm/transparent_hugepage/defrag` such as `always defer defer+madvise [madvise] never`! (but written as just `madvise`)! but as just a boolean `1` or `0` in `/sys/kernel/mm/transparent_hugepage/khugepaged/defrag`. Good old Linux, carrying the flag for consistency and commonsense.
	#[inline(always)]
	pub fn change_transparent_huge_pages_defragmentation(&self, sys_path: &SysPath, pages_to_scan: u16, scan_sleep_in_milliseconds: usize, allocation_sleep_in_milliseconds: usize, how_many_extra_small_pages_not_already_mapped_can_be_allocated_when_collapsing_small_pages: u16, how_many_extra_small_pages_not_already_mapped_can_be_swapped_when_collapsing_small_pages: u16) -> io::Result<()>
	{
		sys_path.khugepaged_file_path("pages_to_scan").write_value(UnpaddedDecimalInteger(pages_to_scan))?;
		sys_path.khugepaged_file_path("alloc_sleep_millisecs").write_value(UnpaddedDecimalInteger(scan_sleep_in_milliseconds))?;
		sys_path.khugepaged_file_path("scan_sleep_millisecs").write_value(UnpaddedDecimalInteger(allocation_sleep_in_milliseconds))?;
		sys_path.khugepaged_file_path("max_ptes_none").write_value(UnpaddedDecimalInteger(how_many_extra_small_pages_not_already_mapped_can_be_allocated_when_collapsing_small_pages))?;
		sys_path.khugepaged_file_path("max_ptes_swap").write_value(UnpaddedDecimalInteger(how_many_extra_small_pages_not_already_mapped_can_be_swapped_when_collapsing_small_pages))?;

		let (transparent_huge_memory_defrag, khugepaged_defrag) = self.to_value();
		sys_path.khugepaged_file_path("defrag").write_value(khugepaged_defrag)?;
		sys_path.transparent_huge_memory_file_path("defrag").write_value(transparent_huge_memory_defrag)?;

		Ok(())
	}
}