atproto relay implementation in zig
zlay.waow.tech
revert exp-001: SmpAllocator grew RSS faster than c_allocator
SmpAllocator RSS grew at ~670 MiB/hour vs c_allocator's ~290 MiB/hour.
disproves glibc fragmentation hypothesis — the leak is genuine.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
+12
-8
+5
-1
EXPERIMENTS.md
+5
-1
EXPERIMENTS.md
···
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log.info("gc: malloc_trim complete", .{});
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```
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-
**status**: active
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**result**: FAILED — RSS grew at ~670 MiB/hour (worse than c_allocator's ~290 MiB/hour).
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this disproves glibc fragmentation as the root cause. the leak is genuine — memory is
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allocated and never freed. reverted to c_allocator.
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**status**: reverted (2026-03-07)
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-7
src/main.zig
+7
-7
src/main.zig
···
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}
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pub fn main() !void {
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// use zig's SmpAllocator — thread-local freelists backed by mmap/munmap.
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// c_allocator (glibc malloc) caused linear RSS growth under cross-thread
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// alloc/free patterns: subscriber threads alloc, worker threads free,
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// glibc's per-thread arenas fragment and never return pages to the OS.
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// see EXPERIMENTS.md exp-001.
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const allocator = std.heap.smp_allocator;
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// use libc allocator (glibc malloc). SmpAllocator was tested (exp-001)
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// and grew RSS even faster — the leak is genuine, not glibc fragmentation.
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const allocator = std.heap.c_allocator;
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// parse config from env
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const port = parseEnvInt(u16, "RELAY_PORT", 3000);
···
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log.info("relay stopped cleanly", .{});
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}
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const malloc_h = @cImport(@cInclude("malloc.h"));
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fn gcLoop(dp: *event_log_mod.DiskPersist) void {
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const gc_interval: u64 = 10 * 60; // 10 minutes in seconds
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while (!shutdown_flag.load(.acquire)) {
···
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log.warn("event log GC failed: {s}", .{@errorName(err)});
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};
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-
log.info("gc: complete", .{});
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_ = malloc_h.malloc_trim(0);
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log.info("gc: malloc_trim complete", .{});
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}
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}
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