hal/linux/LinuxProcessPriority.cpp

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   3  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #include "Hal.h"
   6 #include "HalLog.h"
   7
   8 #include "mozilla/Sprintf.h"
   9 #include "mozilla/Unused.h"
  10
  11 #include <fcntl.h>
  12 #include <unistd.h>
  13
  14 using namespace mozilla::hal;
  15
  16 namespace mozilla::hal_impl {
  17
  18 /* The Linux OOM score is a value computed by the kernel ranging between 0 and
  19  * 1000 and indicating how likely is a process to be killed when memory is
  20  * tight. The larger the value the more likely a process is to be killed. The
  21  * score is computed based on the amount of memory used plus an adjustment
  22  * value. We chose our adjustment values to make it likely that processes are
  23  * killed in the following order:
  24  *
  25  * 1. preallocated processes
  26  * 2. background processes
  27  * 3. background processes playing video (but no audio)
  28  * 4. foreground processes or processes playing or recording audio
  29  * 5. the parent process
  30  *
  31  * At the time of writing (2022) the base score for a process consuming very
  32  * little memory seems to be around ~667. Our adjustments are thus designed
  33  * to ensure this order starting from a 667 baseline but trying not to go too
  34  * close to the 1000 limit where they would be clamped. */
  35
  36 const uint32_t kParentOomScoreAdjust = 0;
  37 const uint32_t kForegroundOomScoreAdjust = 100;
  38 const uint32_t kBackgroundPerceivableOomScoreAdjust = 133;
  39 const uint32_t kBackgroundOomScoreAdjust = 167;
  40 const uint32_t kPreallocOomScoreAdjust = 233;
  41
  42 static uint32_t OomScoreAdjForPriority(ProcessPriority aPriority) {
  43   switch (aPriority) {
  44     case PROCESS_PRIORITY_BACKGROUND:
  45       return kBackgroundOomScoreAdjust;
  46     case PROCESS_PRIORITY_BACKGROUND_PERCEIVABLE:
  47       return kBackgroundPerceivableOomScoreAdjust;
  48     case PROCESS_PRIORITY_PREALLOC:
  49       return kPreallocOomScoreAdjust;
  50     case PROCESS_PRIORITY_FOREGROUND:
  51       return kForegroundOomScoreAdjust;
  52     default:
  53       return kParentOomScoreAdjust;
  54   }
  55 }
  56
  57 void SetProcessPriority(int aPid, ProcessPriority aPriority) {
  58   HAL_LOG("LinuxProcessPriority - SetProcessPriority(%d, %s)\n", aPid,
  59           ProcessPriorityToString(aPriority));
  60
  61   uint32_t oomScoreAdj = OomScoreAdjForPriority(aPriority);
  62
  63   char path[32] = {};
  64   SprintfLiteral(path, "/proc/%d/oom_score_adj", aPid);
  65
  66   char oomScoreAdjStr[11] = {};
  67   SprintfLiteral(oomScoreAdjStr, "%d", oomScoreAdj);
  68
  69   int fd = open(path, O_WRONLY);
  70   if (fd < 0) {
  71     return;
  72   }
  73   const size_t len = strlen(oomScoreAdjStr);
  74   Unused << write(fd, oomScoreAdjStr, len);
  75   Unused << close(fd);
  76 }
  77
  78 }  // namespace mozilla::hal_impl