Add backend memory usage comparison action for PRs (#16926)

* Initial plan

* Add backend memory usage comparison action

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

* Fix deprecated serverProcess.killed usage

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

* Add explicit permissions to save-pr-number job

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

* Change PR comment text from Japanese to English

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

* Inline memory measurement script to fix base ref compatibility

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

* Revert "Inline memory measurement script to fix base ref compatibility"

This reverts commit 6f76a121efd450c257167cce6e298c59936f4e37.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

1 files changed, 152 insertions, 0 deletions

diff --git a/packages/backend/scripts/measure-memory.mjs b/packages/backend/scripts/measure-memory.mjs
new file mode 100644
index 0000000000..017252d7ec
--- /dev/null
+++ b/packages/backend/scripts/measure-memory.mjs
@@ -0,0 +1,152 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+/**
+ * This script starts the Misskey backend server, waits for it to be ready,
+ * measures memory usage, and outputs the result as JSON.
+ *
+ * Usage: node scripts/measure-memory.mjs
+ */
+
+import { fork } from 'node:child_process';
+import { setTimeout } from 'node:timers/promises';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const STARTUP_TIMEOUT = 120000; // 120 seconds timeout for server startup
+const MEMORY_SETTLE_TIME = 10000; // Wait 10 seconds after startup for memory to settle
+
+async function measureMemory() {
+	const startTime = Date.now();
+
+	// Start the Misskey backend server using fork to enable IPC
+	const serverProcess = fork(join(__dirname, '../built/boot/entry.js'), [], {
+		cwd: join(__dirname, '..'),
+		env: {
+			...process.env,
+			NODE_ENV: 'test',
+		},
+		stdio: ['pipe', 'pipe', 'pipe', 'ipc'],
+	});
+
+	let serverReady = false;
+
+	// Listen for the 'ok' message from the server indicating it's ready
+	serverProcess.on('message', (message) => {
+		if (message === 'ok') {
+			serverReady = true;
+		}
+	});
+
+	// Handle server output
+	serverProcess.stdout?.on('data', (data) => {
+		process.stderr.write(`[server stdout] ${data}`);
+	});
+
+	serverProcess.stderr?.on('data', (data) => {
+		process.stderr.write(`[server stderr] ${data}`);
+	});
+
+	// Handle server error
+	serverProcess.on('error', (err) => {
+		process.stderr.write(`[server error] ${err}\n`);
+	});
+
+	// Wait for server to be ready or timeout
+	const startupStartTime = Date.now();
+	while (!serverReady) {
+		if (Date.now() - startupStartTime > STARTUP_TIMEOUT) {
+			serverProcess.kill('SIGTERM');
+			throw new Error('Server startup timeout');
+		}
+		await setTimeout(100);
+	}
+
+	const startupTime = Date.now() - startupStartTime;
+	process.stderr.write(`Server started in ${startupTime}ms\n`);
+
+	// Wait for memory to settle
+	await setTimeout(MEMORY_SETTLE_TIME);
+
+	// Get memory usage from the server process via /proc
+	const pid = serverProcess.pid;
+	let memoryInfo;
+
+	try {
+		const fs = await import('node:fs/promises');
+
+		// Read /proc/[pid]/status for detailed memory info
+		const status = await fs.readFile(`/proc/${pid}/status`, 'utf-8');
+		const vmRssMatch = status.match(/VmRSS:\s+(\d+)\s+kB/);
+		const vmDataMatch = status.match(/VmData:\s+(\d+)\s+kB/);
+		const vmSizeMatch = status.match(/VmSize:\s+(\d+)\s+kB/);
+
+		memoryInfo = {
+			rss: vmRssMatch ? parseInt(vmRssMatch[1], 10) * 1024 : null,
+			heapUsed: vmDataMatch ? parseInt(vmDataMatch[1], 10) * 1024 : null,
+			vmSize: vmSizeMatch ? parseInt(vmSizeMatch[1], 10) * 1024 : null,
+		};
+	} catch (err) {
+		// Fallback: use ps command
+		process.stderr.write(`Warning: Could not read /proc/${pid}/status: ${err}\n`);
+
+		const { execSync } = await import('node:child_process');
+		try {
+			const ps = execSync(`ps -o rss= -p ${pid}`, { encoding: 'utf-8' });
+			const rssKb = parseInt(ps.trim(), 10);
+			memoryInfo = {
+				rss: rssKb * 1024,
+				heapUsed: null,
+				vmSize: null,
+			};
+		} catch {
+			memoryInfo = {
+				rss: null,
+				heapUsed: null,
+				vmSize: null,
+				error: 'Could not measure memory',
+			};
+		}
+	}
+
+	// Stop the server
+	serverProcess.kill('SIGTERM');
+
+	// Wait for process to exit
+	let exited = false;
+	await new Promise((resolve) => {
+		serverProcess.on('exit', () => {
+			exited = true;
+			resolve(undefined);
+		});
+		// Force kill after 10 seconds if not exited
+		setTimeout(10000).then(() => {
+			if (!exited) {
+				serverProcess.kill('SIGKILL');
+			}
+			resolve(undefined);
+		});
+	});
+
+	const result = {
+		timestamp: new Date().toISOString(),
+		startupTimeMs: startupTime,
+		memory: memoryInfo,
+	};
+
+	// Output as JSON to stdout
+	console.log(JSON.stringify(result, null, 2));
+}
+
+measureMemory().catch((err) => {
+	console.error(JSON.stringify({
+		error: err.message,
+		timestamp: new Date().toISOString(),
+	}));
+	process.exit(1);
+});