Mojo LSP (mojo-lsp-server) consumes ~13GB RAM then OOM-killed / sometimes segfaults when opening MMMAudio workspace

[chilichesdog]

Environment

OS: Ubuntu 24.04.1 (kernel 6.17.0-14-generic), x86_64
VS Code: 1.109.5 (commit 072586267e68ece9a47aa43f8c108e0dcbf44622)
Mojo VS Code extension: modular-mojotools.vscode-mojo@26.2.0
Mojo toolchain used for project: mojo==0.25.6.1 (installed via pip into venv; MMMAudio main branch is tied to 0.25.6.1)
Python: 3.12.3
Project/workspace: https://github.com/spluta/MMMAudio at commit 0f9d24caadc38d41f1c248c5e7fce76afbde651c

What happens

When opening the MMMAudio workspace in VS Code, the Mojo language server process mojo-lsp-server steadily grows in memory usage until the system becomes sluggish/unresponsive, and then the Linux OOM killer terminates mojo-lsp-server. In one run, mojo-lsp-server also segfaulted prior to OOM.

This causes Mojo IDE features to stop working (hover/highlighting/completions) and VS Code may appear to “crash”/freeze due to system-wide memory pressure.
Evidence (kernel logs)

From sudo dmesg -T:

less
[Thu Mar 12 17:04:28 2026] 🔥 Thread2[15329]: segfault at 5c222084d000 ip 00005c1e37eb16f0 sp 000078ecc7ffd940 error 4 in mojo-lsp-server[9576f0,5c1e37dc8000+13c8000] likely on CPU 7 (core 12, socket 0)

[Thu Mar 12 17:07:25 2026] VizCompositorTh invoked oom-killer: gfp_mask=0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), order=0, oom_score_adj=200
[Thu Mar 12 17:07:25 2026] [ 15321] 1000 15321 5207860 3351645 3351517 128 0 35373056 700800 100 mojo-lsp-server
[Thu Mar 12 17:07:25 2026] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-1000.slice/user@1000.service/app.slice/app-org.chromium.Chromium-14557.scope,task=mojo-lsp-server,pid=15321,uid=1000
[Thu Mar 12 17:07:25 2026] Out of memory: Killed process 15321 (mojo-lsp-server) total-vm:20831440kB, anon-rss:13406068kB, file-rss:512kB, shmem-rss:0kB, UID:1000 pgtables:34544kB oom_score_adj:100

(anon-rss ~13.4GB)
Steps to reproduce

Install modular-mojotools.vscode-mojo@26.2.0
Clone MMMAudio and open the repo root in VS Code:
    git clone https://github.com/spluta/MMMAudio
    open folder in VS Code
Wait for Mojo language features to initialize / indexing to occur; open a .mojo file and/or trigger hover/completions
Observe mojo-lsp-server memory growth; system becomes sluggish; eventually OOM kills mojo-lsp-server (see dmesg above)

Expected

Mojo LSP remains stable and bounded in memory usage
No segfaults
VS Code remains responsive, Mojo language features continue to work

Actual

mojo-lsp-server memory grows without bound (eventually ~13GB anon RSS)
System becomes sluggish/unresponsive
Kernel OOM killer terminates mojo-lsp-server
Sometimes mojo-lsp-server segfaults

Notes

This may be related to workspace indexing scope. In earlier experiments, having a large in-workspace Python venv/ (many GB) seemed to exacerbate the issue. Even after moving the venv outside the repo, the issue still reproduces.