Add setting of oom_score_adj (#1504)

To limit risk of killing by OOM Killer.

src/mergerfs.cpp

@@ -23,13 +23,14 @@
 #include "fs_umount2.hpp"
 #include "fs_wait_for_mount.hpp"
 #include "gidcache.hpp"
+#include "maintenance_thread.hpp"
+#include "oom.hpp"
 #include "option_parser.hpp"
 #include "procfs.hpp"
 #include "resources.hpp"
 #include "strvec.hpp"
 #include "syslog.hpp"
 #include "version.hpp"
-#include "maintenance_thread.hpp"
 
 #include "fuse_access.hpp"
 #include "fuse_bmap.hpp"
@@ -164,6 +165,27 @@ namespace l
     resources::setpriority(scheduling_priority_);
   }
 
+  static
+  void
+  set_oom_score_adj()
+  {
+    int rv;
+    int orig;
+    int score;
+
+    if(!oom::has_oom_score_adj())
+      return;
+
+    score = -990;
+
+    orig = oom::get_oom_score_adj();
+    rv   = oom::set_oom_score_adj(score);
+
+    SysLog::info("set oom_score_adj to {}, originally {}",
+                 score,
+                 orig);
+  }
+
   static
   bool
   wait_for_mount(const Config::Read &cfg_)
@@ -318,6 +340,7 @@ namespace l
     });
     l::setup_resources(cfg->scheduling_priority);
     l::setup_signal_handlers();
+    l::set_oom_score_adj();
     l::get_fuse_operations(ops,cfg->nullrw);
 
     if(cfg->lazy_umount_mountpoint)

src/oom.cpp

@@ -0,0 +1,68 @@
+/*
+  ISC License
+
+  Copyright (c) 2025, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "oom.hpp"
+
+#include "fs_exists.hpp"
+
+#include "fmt/core.h"
+
+#include <fstream>
+#include <tuple>
+
+
+constexpr char SELF_OOM_SCORE_ADJ[] = "/proc/self/oom_score_adj";
+
+bool
+oom::has_oom_score_adj()
+{
+  return fs::exists(SELF_OOM_SCORE_ADJ);
+}
+
+int
+oom::get_oom_score_adj()
+{
+  int score;
+  std::ifstream ifs;
+
+  ifs.open(SELF_OOM_SCORE_ADJ);
+  if(!ifs)
+    return 0;
+
+  ifs >> score;
+
+  ifs.close();
+
+  return score;
+}
+
+int
+oom::set_oom_score_adj(const int score_)
+{
+  std::ofstream ofs;
+
+  ofs.open(SELF_OOM_SCORE_ADJ);
+  if(!ofs)
+    return -errno;
+
+  ofs << fmt::format("{}",score_);
+
+  ofs.close();
+
+  return 0;
+}

src/oom.hpp

@@ -0,0 +1,27 @@
+/*
+  ISC License
+
+  Copyright (c) 2025, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+
+namespace oom
+{
+  bool has_oom_score_adj();
+  int  get_oom_score_adj();
+  int  set_oom_score_adj(const int score);
+};