zzstoatzz.io
atproto relay implementation in zig
zlay.waow.tech
fix: use mallinfo2 via extern decl for accurate metrics >2 GiB
mallinfo's int fields were overflowing at 2 GiB, making arena and
mmap metrics useless. the runtime glibc (2.36) has mallinfo2 but
zig's bundled cross-compile headers don't declare it. manual extern
struct declaration bypasses the header issue.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
+17
-4
src/broadcaster.zig
+17
-4
src/broadcaster.zig
···
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return fbs.getWritten();
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}
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-
const malloc_h = @cImport(@cInclude("malloc.h"));
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// glibc mallinfo2 (available since 2.33) — declared manually because zig's
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// bundled cross-compile headers may not include it, but the runtime glibc does.
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// uses usize fields (no 2 GiB overflow like mallinfo's int fields).
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const Mallinfo2 = extern struct {
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arena: usize, // bytes claimed from OS (non-mmap)
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ordblks: usize,
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smblks: usize,
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hblks: usize,
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hblkhd: usize, // bytes in mmap regions
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usmblks: usize,
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fsmblks: usize,
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uordblks: usize, // bytes in use (allocated)
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fordblks: usize, // free bytes in arena (fragmentation)
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keepcost: usize,
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};
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extern "c" fn mallinfo2() Mallinfo2;
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fn appendProcMetrics(w: anytype) void {
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// RSS from /proc/self/statm (field[1] * page_size)
···
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} else |_| {}
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// glibc malloc arena stats — distinguishes in-use heap from fragmentation
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// uses mallinfo (not mallinfo2) for older glibc compat; int fields cap at 2 GiB
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// but that's enough to distinguish leak vs fragmentation patterns
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const mi = malloc_h.mallinfo();
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const mi = mallinfo2();
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std.fmt.format(w,
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\\# TYPE relay_malloc_arena_bytes gauge
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\\# HELP relay_malloc_arena_bytes total bytes claimed from OS by malloc