kill: when we have swap space, give the kernel extra time

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.
(Yes, this will sleep even if the kill has failed. Does no harm and keeps the
code simple.)

Makefile

@@ -71,7 +71,8 @@ uninstall-initscript: uninstall-bin
 uninstall-bin:
 	rm -f $(DESTDIR)$(PREFIX)$(BINDIR)/earlyoom
 
-format:
+# Depends on earlyoom compilation to make sure the syntax is ok.
+format: earlyoom
 	clang-format -i *.h *.c
 
 test: earlyoom

main.c

@@ -254,6 +254,7 @@ int main(int argc, char* argv[])
             perror("Could not set oom_score_adj to -1000 for earlyoom process - continuing anyway");
     }
 
+    int tick_us = 100000; // 100 ms <=> 10 Hz
     c = 0; // loop counter
     report_interval = report_interval * 10; // loop runs at 10Hz
     while (1) {
@@ -265,10 +266,20 @@ int main(int argc, char* argv[])
             handle_oom(procdir, 9, kernel_oom_killer, ignore_oom_score_adj,
                 notif_command, prefer_regex, avoid_regex);
             oom_cnt++;
+            // 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.
+            // (Yes, this will sleep even if the kill has failed. Does no harm and keeps the
+            // code simple.)
+            if (m.SwapTotalMiB > 0) {
+                int sleep_cycles = 2;
+                usleep(sleep_cycles * tick_us);
+                c += sleep_cycles;
+            }
         } else if (report_interval > 0 && c % report_interval == 0) {
             print_mem_stats(stdout, m);
         }
-        usleep(100000); // 100 ms <=> 10 Hz
+        usleep(tick_us);
         c++;
     }
     return 0;