Fix CSV path joining and relative exclusions; add scan benchmark script

DEVELOPMENT.md

@@ -21,6 +21,26 @@ bin/treegen --out /tmp/t --directories 50000 --files 1000000 --max-depth 20 --sp
 bin/mapsize /tmp/t
 ```
 
+## Benchmarks
+
+```sh
+make benchmark                          # Go micro-benchmarks (layout, render, filter, scan)
+scripts/bench-scan.sh /path 1 2 4 8     # wall time and peak RSS per worker count
+sudo DROP_CACHES=1 scripts/bench-scan.sh /path   # cold-cache runs
+MAPSIZE_MEM_ROOT=/path go test ./internal/scan -run TestMemoryPerNode -v
+```
+
+Paste results into PERFORMANCE.md with the machine description. Never edit
+numbers by hand.
+
+## Terminal restoration checks
+
+```sh
+MAPSIZE_DEBUG_PANIC=ui bin/mapsize .        # panics on the first key press
+MAPSIZE_DEBUG_PANIC=scanner bin/mapsize /   # panics in a scanner goroutine
+stty -a                                     # echo/icanon must be back on
+```
+
 ## Profiling
 
 ```sh

internal/export/export.go

@@ -8,6 +8,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"path/filepath"
 	"strconv"
 	"time"
 
@@ -158,7 +159,7 @@ func CSV(w io.Writer, t *inventory.Tree, root inventory.NodeID, maxDepth int) er
 			return nil
 		}
 		for _, c := range t.SortedChildren(id, inventory.SizeAllocated) {
-			if err := rec(c, path+"/"+t.Node(c).Name, depth-1); err != nil {
+			if err := rec(c, filepath.Join(path, t.Node(c).Name), depth-1); err != nil {
 				return err
 			}
 		}

internal/scan/scan.go

@@ -138,6 +138,17 @@ type inodeKey struct{ dev, ino uint64 }
 // Start stats root, creates the tree and begins scanning in the background.
 func Start(ctx context.Context, root string, opts Options) (*Scanner, error) {
 	opts.defaults()
+	// Path-style exclusions are matched against absolute paths.
+	excl := make([]string, len(opts.Excludes))
+	for i, p := range opts.Excludes {
+		excl[i] = p
+		if strings.ContainsAny(p, `/\`) {
+			if a, err := filepath.Abs(p); err == nil {
+				excl[i] = a
+			}
+		}
+	}
+	opts.Excludes = excl
 	abs, err := filepath.Abs(root)
 	if err != nil {
 		return nil, err

internal/scan/scan_test.go

@@ -237,6 +237,12 @@ func TestExcludes(t *testing.T) {
 	if tr.Stats.Excluded != 2 || tr.Node(0).Files != 1 {
 		t.Fatalf("excluded=%d files=%d", tr.Stats.Excluded, tr.Node(0).Files)
 	}
+	// Relative path patterns resolve against the working directory.
+	t.Chdir(root)
+	tr = runScan(t, root, Options{Workers: 2, Excludes: []string{"./skip"}})
+	if tr.Stats.Excluded != 1 {
+		t.Fatalf("relative exclude: excluded=%d", tr.Stats.Excluded)
+	}
 }
 
 func TestUnicodeAndHostileNames(t *testing.T) {

scripts/bench-scan.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Records scan benchmarks as Markdown table rows for PERFORMANCE.md.
+#
+#   scripts/bench-scan.sh PATH [workers...]      (default workers: 1 2 4 8 16)
+#
+# Linux only (uses /usr/bin/time, df, lsblk). Runs each configuration three
+# times against a warm cache; to measure a cold cache, run as root with
+# DROP_CACHES=1, which drops the page cache before every run.
+set -euo pipefail
+path=${1:?usage: bench-scan.sh PATH [workers...]}
+shift || true
+workers=${*:-1 2 4 8 16}
+bin=${MAPSIZE:-bin/mapsize}
+[[ -x $bin ]] || make build >/dev/null
+
+fs=$(df -T "$path" | awk 'NR==2 {print $2}')
+dev=$(df "$path" | awk 'NR==2 {print $1}')
+medium=$(lsblk -no ROTA "$dev" 2>/dev/null | head -1 | sed 's/1/rotational/;s/0/solid-state/')
+counts=$("$bin" --no-ui "$path" 2>/dev/null | awk '/^Files/ {f=$2} /^Directories/ {d=$2} END {print f" files, "d" dirs"}')
+
+echo "<!-- $(date -u +%FT%TZ) $(uname -srm), $(nproc) CPUs -->"
+echo "Path: \`$path\` · $fs on ${medium:-unknown medium} · $counts"
+echo
+echo "| workers | cache | wall (s) | peak RSS (MB) |"
+echo "|---:|---|---:|---:|"
+for w in $workers; do
+  for i in 1 2 3; do
+    cache=warm
+    if [[ ${DROP_CACHES:-} == 1 ]]; then
+      sync; echo 3 > /proc/sys/vm/drop_caches; cache=cold
+    fi
+    out=$( { /usr/bin/time -f "%e %M" "$bin" --no-ui --workers "$w" "$path" >/dev/null; } 2>&1 | tail -1)
+    read -r secs kb <<<"$out"
+    echo "| $w | $cache | $secs | $((kb / 1024)) |"
+  done
+done