Remove option to use kernel oom-killer (-k)

The kernel oom-killer has many problems, has no
features, and is probably used by nobody at all.

Quoting from the (remove) function comment:

 * Invoke the kernel oom killer by writing "f" into /proc/sysrq-trigger
 *
 * This approach has a few problems:
 * 1) It is disallowed by default (even for root) on Fedora 20.
 *    You have to first write "1" into /proc/sys/kernel/sysrq to enable the "f"
 *    trigger.
 * 2) The Chrome web browser assigns a penalty of 300 onto its own tab renderer
 *    processes. On an 8GB RAM machine, this means 2400MB, and will lead to every
 *    tab being killed before the actual memory hog
 *    See https://code.google.com/p/chromium/issues/detail?id=333617 for more info
 * 3) It is broken in 4.0.5 - see
 *    f7e2ced

#80

MANPAGE.md

@@ -37,7 +37,7 @@ set available memory minimum to SIZE KiB
 set free swap minimum to SIZE KiB
 
 #### -k
-use kernel oom killer instead of own user-space implementation
+removed in earlyoom v1.2, ignored for compatibility
 
 #### -i
 user-space oom killer should ignore positive oom_score_adj values

README.md

@@ -204,6 +204,8 @@ accept
 
 Changelog
 ---------
+* v1.2, in progress
+  * Remove option to use kernel oom-killer (`-k`) ([issue #80](https://github.com/rfjakob/earlyoom/issues/80))
 * v1.1, 2018-07-07
   * Fix possible shell code injection through GUI notifications
     ([commit](https://github.com/rfjakob/earlyoom/commit/ab79aa3895077676f50120f15e2bb22915446db9))

kill.c

@@ -118,7 +118,7 @@ static struct procinfo get_process_stats(int pid)
  * Find the process with the largest oom_score and kill it.
  * See trigger_kernel_oom() for the reason why this is done in userspace.
  */
-static void userspace_kill(poll_loop_args_t args, int sig)
+void userspace_kill(poll_loop_args_t args, int sig)
 {
     struct dirent* d;
     char buf[256];
@@ -243,49 +243,3 @@ static void userspace_kill(poll_loop_args_t args, int sig)
         sleep(1);
     }
 }
-
-/*
- * Invoke the kernel oom killer by writing "f" into /proc/sysrq-trigger
- *
- * This approach has a few problems:
- * 1) It is disallowed by default (even for root) on Fedora 20.
- *    You have to first write "1" into /proc/sys/kernel/sysrq to enable the "f"
- *    trigger.
- * 2) The Chrome web browser assigns a penalty of 300 onto its own tab renderer
- *    processes. On an 8GB RAM machine, this means 2400MB, and will lead to every
- *    tab being killed before the actual memory hog
- *    See https://code.google.com/p/chromium/issues/detail?id=333617 for more info
- * 3) It is broken in 4.0.5 - see
- *    https://github.com/rfjakob/earlyoom/commit/f7e2cedce8e9605c688d0c6d7dc26b7e81817f02
- * Because of these issues, kill_by_rss() is used instead by default.
- */
-void trigger_kernel_oom(int sig, char* notif_command)
-{
-    FILE* trig_fd;
-    trig_fd = fopen("sysrq-trigger", "w");
-    if (trig_fd == NULL) {
-        perror("Could not open /proc/sysrq-trigger");
-        exit(7);
-    }
-    if (sig == 9) {
-        fprintf(stderr, "Invoking oom killer: ");
-        maybe_notify(notif_command,
-            "-i dialog-warning 'earlyoom' 'Invoking OOM killer'");
-
-        if (fprintf(trig_fd, "f\n") != 2) {
-            perror("failed");
-            maybe_notify(notif_command,
-                "-i dialog-error 'earlyoom' 'Error: Failed to invoke OOM killer'");
-        } else
-            fprintf(stderr, "done\n");
-    }
-    fclose(trig_fd);
-}
-
-void handle_oom(poll_loop_args_t args, int sig)
-{
-    if (args.kernel_oom_killer)
-        trigger_kernel_oom(sig, args.notif_command);
-    else
-        userspace_kill(args, sig);
-}

kill.h

@@ -9,8 +9,6 @@ typedef struct {
      * we start killing processes */
     int mem_min_percent;
     int swap_min_percent;
-    /* use the kernel oom killer? */
-    bool kernel_oom_killer;
     /* ignore /proc/PID/oom_score_adj? */
     bool ignore_oom_score_adj;
     /* notifcation command to launch when killing something. NULL = no-op. */
@@ -22,4 +20,4 @@ typedef struct {
     int report_interval_ms;
 } poll_loop_args_t;
 
-void handle_oom(poll_loop_args_t args, int sig);
+void userspace_kill(poll_loop_args_t args, int sig);

main.c

@@ -111,8 +111,7 @@ int main(int argc, char* argv[])
             }
             break;
         case 'k':
-            args.kernel_oom_killer = 1;
-            fprintf(stderr, "Using kernel oom killer\n");
+            fprintf(stderr, "Option -k is ignored since earlyoom v1.2\n");
             break;
         case 'i':
             args.ignore_oom_score_adj = 1;
@@ -155,7 +154,6 @@ int main(int argc, char* argv[])
                 "  -s PERCENT       set free swap minimum to PERCENT of total (default 10 %%)\n"
                 "  -M SIZE          set available memory minimum to SIZE KiB\n"
                 "  -S SIZE          set free swap minimum to SIZE KiB\n"
-                "  -k               use kernel oom killer instead of own user-space implementation\n"
                 "  -i               user-space oom killer should ignore positive oom_score_adj values\n"
                 "  -n               enable notifications using \"notify-send\"\n"
                 "  -N COMMAND       enable notifications using COMMAND\n"
@@ -184,16 +182,6 @@ int main(int argc, char* argv[])
         exit(2);
     }
 
-    if (args.kernel_oom_killer && args.ignore_oom_score_adj) {
-        fprintf(stderr, "Kernel oom killer does not support -i\n");
-        exit(2);
-    }
-
-    if (args.kernel_oom_killer && (prefer_cmds || avoid_cmds)) {
-        fprintf(stderr, "Kernel oom killer does not support --prefer/--avoid\n");
-        exit(2);
-    }
-
     if (prefer_cmds) {
         args.prefer_regex = &_prefer_regex;
         if (regcomp(args.prefer_regex, prefer_cmds, REG_EXTENDED | REG_NOSUB) != 0) {
@@ -250,7 +238,7 @@ int main(int argc, char* argv[])
     /* Dry-run oom kill to make sure stack grows to maximum size before
      * calling mlockall()
      */
-    handle_oom(args, 0);
+    userspace_kill(args, 0);
 
     if (mlockall(MCL_CURRENT | MCL_FUTURE) != 0)
         perror("Could not lock memory - continuing anyway");
@@ -321,7 +309,7 @@ static void poll_loop(const poll_loop_args_t args)
                 m.SwapTotalMiB,
                 m.SwapFreePercent,
                 args.swap_min_percent);
-            handle_oom(args, 9);
+            userspace_kill(args, 9);
             // With swap enabled, the kernel seems to need more than 100ms to free the memory
             // of the killed process. This means that earlyoom would immediately kill another
             // process. Sleep a little extra to give the kernel time to free the memory.