Builder: a warning for Linux before 6.7, compile jobs as many as the RAM holds, temporary files in the game folder

- hw_check.py kernel_old: below 6.7 the game has no write watch (userfaultfd WP_ASYNC, PAGEMAP_SCAN) and copies whole
  pools before each submission.
- build_game.py: jobs up to 80 % of the RAM at 768 MiB each (as totk-pc-recomp), within --cpus.
- setup.py on Linux: TMPDIR is temp/ of the game folder (a Steam Deck's /tmp is memory, /home small).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tools/build_game.py

@@ -150,7 +150,7 @@ def main():
         game_cflags = game_cflags.replace(' -gcodeview', '') + ' ' + linux_flags()
     if arch != 'x86-64-v3':
         print(f'code for {arch}: this CPU has no AVX2 / FMA / BMI2 (slower than x86-64-v3)', flush=True)
-    a.j = a.j or a.cpus
+    a.j = a.j or min(a.cpus, jobs_for_ram())
     gen = ROOT / a.generated
     bd = 'build-linux' if linux else 'build'
     build = ROOT / bd
@@ -271,6 +271,14 @@ def main():
     sys.exit(rc)
 
 
+def jobs_for_ram():
+    """As many clang processes as the memory holds: up to 768 MiB each, in 80 % of the RAM (as totk-pc-recomp's
+    build_game.py; the largest generated files take about that). 8 GB of RAM: 8, a Steam Deck's 16 GB: 16."""
+    import hw_check
+    ram = hw_check.ram_bytes()
+    return max(1, int(ram * 0.8) // (768 << 20)) if ram else 64
+
+
 def run_limited(cmd, env, mask, on_line=None):
     """cmd at below-normal priority on the CPUs in mask; on_line(line): its output line by line instead of the console.
     Linux: nice 10 and the CPUs set in the child before it starts, which every clang it starts inherits (as PR #42)."""

tools/hw_check.py

@@ -13,6 +13,7 @@ goes on; 'info': a remark. The launcher has the texts for the codes in its langu
   vram_low          gpu, gb       warn   less than 4 GB of video memory
   ram_low           gb            warn   less than 16 GB of RAM
   cpu_no_avx2                     warn   the code is built for SSE4.2 (slower)
+  kernel_old        version       warn   Linux below 6.7: no write watch for the game's memory (very slow)
   disk_space        need_gb, free_gb, drive   block
   amd_untested      gpu           info   [temporary] AMD cards are not tested yet (dev-local/docs/issues.md, "#2, #16,
                                          #23"): remove once players with RDNA report that the game runs
@@ -137,9 +138,25 @@ def cases(folder, platforms=('windows',)):
             out.append({'code': 'ram_low', 'sev': 'warn', 'args': {'gb': round(ram / 2**30)}})
         if not avx2():
             out.append({'code': 'cpu_no_avx2', 'sev': 'warn', 'args': {}})
+    if os.name != 'nt' and kernel_version() < KERNEL_WRITE_WATCH:   # the game is built where it runs
+        out.append({'code': 'kernel_old', 'sev': 'warn', 'args': {'version': os.uname().release}})
     return out + disk_case(folder, 'linux' in platforms)
 
 
+KERNEL_WRITE_WATCH = (6, 7)   # userfaultfd write protection without faults (WP_ASYNC) and PAGEMAP_SCAN
+
+
+def kernel_version():
+    """Linux's version as numbers ((0, 0): unknown, as when not Linux). Below 6.7 the game has no write watch
+    (src/runtime/platform/linux.c): every pool the GPU uses is copied whole before each submission, very slow (as
+    totk-pc-recomp warns, installer/steps.py). SteamOS 3.8 and later have 6.11+."""
+    try:
+        parts = os.uname().release.split('-')[0].split('.')
+        return tuple(int(p) for p in parts[:2])
+    except (AttributeError, ValueError):
+        return (0, 0)
+
+
 def text(case):
     """An English line for the console (the launcher has its own texts)."""
     a = case['args']
@@ -153,6 +170,7 @@ def text(case):
         'vram_low': f'{a.get("gpu")} has {a.get("gb")} GB of video memory; 4 GB or more is recommended',
         'ram_low': f'this PC has {a.get("gb")} GB of RAM; 16 GB or more is recommended',
         'cpu_no_avx2': 'the CPU lacks AVX2: the game is built for SSE4.2 and runs a little slower',
+        'kernel_old': f'Linux {a.get("version")}: 6.7 or newer is needed, else the game cannot track its memory writes and runs very slowly; update the system',
         'disk_space': f'the build needs {a.get("need_gb")} GB on {a.get("drive")}, {a.get("free_gb")} GB is free',
         'amd_untested': f'{a.get("gpu")}: AMD cards are not tested yet; please report how the game runs',
     }.get(case['code'], case['code'])

tools/setup.py

@@ -657,6 +657,11 @@ def main():
         state['platforms'] = PLATFORMS[a.platform]
     state.setdefault('platforms', ['windows'])
     if os.name != 'nt':   # Linux builds the game for Linux, here
+        # The tools' temporary files in the game's folder (temp/): on a Steam Deck /tmp is memory and /home small
+        # (totk-pc-recomp's installer puts its temp folder beside the game for the same reason)
+        tmp = ROOT / 'temp'
+        tmp.mkdir(exist_ok=True)
+        os.environ['TMPDIR'] = str(tmp)
         if a.platform and a.platform != 'linux':
             fail_tools(deps_install.DepsError('on Linux UltraTears is built for Linux: --platform linux'))
         state['platforms'] = ['linux']