jschoubben
3a84044ece
With THP 'always' journald's mmapped journal files sit in 2 MiB folios, so each small journal write dirties and writes back 2 MiB; on the control node that saturated the root mirror holding the bus store and the store, and the controller lost its lease. The module sets the mode from a per-machine setting (default always, the kernel's own, so assigning it changes nothing until a machine sets madvise), verifies it took, rotates the journal once so new files are mapped under the new mode, gives back what it found when stopped, and serves kernel_huge_pages to measure file_thp per unit.
51 lines
2.0 KiB
Go
51 lines
2.0 KiB
Go
// The kernel module's tools bundle (novox/hq to-be 42 Phase 1 row 11, issue 746).
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//
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// Served by the node's runtime over MCP on stdio through the Go SDK (ADR 0188, ADR 0193). It only reads:
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// the transparent huge pages the kernel runs with, and which units hold file pages in huge folios, which
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// is what a small write to a mapped file costs a whole huge page of writeback for (issue 746).
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package main
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import (
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"fmt"
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"os"
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stdio "git.novox.be/novox/mesh-sdk/go"
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)
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// binaryName is what the build names this bundle's executable: the manifest's `binary`.
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const binaryName = "kernel-tools"
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func main() {
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// An empty name serves as the module the runtime names (MESH_SERVED_MODULE): kernel.
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if err := stdio.Serve("", tools(ThisMachine())); err != nil {
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fmt.Fprintln(os.Stderr, err)
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os.Exit(1)
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}
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}
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func tools(m *Machine) []stdio.Tool {
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return []stdio.Tool{
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{
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Name: "kernel_huge_pages",
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Description: "Transparent huge pages on this machine: the mode in force (always, madvise or never) and defrag, " +
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"each per-size control with what inherit resolves to, the machine's huge pages by kind (anonymous, " +
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"shared memory, file, file mapped at 2 MiB) from /proc/meminfo, and the units holding the most file " +
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"pages in huge folios (memory.stat file_thp) with their dirty and writeback bytes and the bytes their " +
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"cgroup has written (io.stat, the most any one device saw). A unit with file_thp that writes far more " +
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"than its files grow is paying a whole huge page of writeback per small write (novox/hq issue 746). " +
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"Replaces cat /sys/kernel/mm/transparent_hugepage/enabled, grep Huge /proc/meminfo and reading " +
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"memory.stat by hand. (r)",
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Input: schema(map[string]any{
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"units": map[string]any{"type": "integer", "description": "how many units to name, the most file_thp first (default 10, 0 for none, at most 100)"},
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}),
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Run: func(args map[string]any) (any, error) {
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n, err := whole(args, "units", 10, 0, 100)
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if err != nil {
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return nil, err
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}
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return m.HugePages(n)
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},
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},
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}
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}
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