atproto relay implementation in zig
zlay.waow.tech
use page_allocator for per-frame arenas to fix linear RSS growth
glibc malloc was not returning freed arena pages to the OS under
high-churn multi-thread load (~700 frames/sec across 2250+ subscriber
threads + 16 worker threads), causing linear RSS growth from 0 to
~3.5 GiB over 12h despite correct defer arena.deinit() everywhere.
page_allocator uses mmap/munmap directly — pages are guaranteed to
return to the OS on deinit(). ArenaAllocator batches small allocs
into chunks, so actual mmap calls per frame are ~1-3 (negligible).
long-lived state (caches, DB, ring buffer) stays on c_allocator.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
+7
-5
+1
-1
src/frame_worker.zig
+1
-1
src/frame_worker.zig
···
33
33
pub fn processFrame(work: *FrameWork) void {
34
34
defer work.allocator.free(work.data);
35
35
36
-
var arena = std.heap.ArenaAllocator.init(work.allocator);
36
+
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
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defer arena.deinit();
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const alloc = arena.allocator();
39
39
+5
-3
src/main.zig
+5
-3
src/main.zig
···
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119
}
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pub fn main() !void {
122
-
// use libc allocator — glibc malloc has per-thread arenas, madvise-based page
123
-
// return, and proven fragmentation mitigation. GPA is a debug allocator that
124
-
// tracks per-allocation metadata and never returns freed pages to the OS.
122
+
// use libc allocator for long-lived state (caches, DB connections, host maps).
123
+
// per-frame ArenaAllocators use page_allocator instead — glibc malloc was not
124
+
// returning freed arena pages to the OS under high-churn multi-thread load,
125
+
// causing linear RSS growth (~3.5 GiB over 12h). page_allocator uses mmap/munmap
126
+
// directly, guaranteeing page return on arena.deinit().
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const allocator = std.heap.c_allocator;
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// parse config from env
+1
-1
src/subscriber.zig
+1
-1
src/subscriber.zig
···
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const sub = self.subscriber;
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258
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259
// lightweight header decode for cursor tracking + routing
260
-
var arena = std.heap.ArenaAllocator.init(sub.allocator);
260
+
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
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defer arena.deinit();
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262
const alloc = arena.allocator();
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263