tor-browser

The Tor Browser
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LinuxProcessPriority.cpp (2843B)

      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 
     10 #include <fcntl.h>
     11 #include <unistd.h>
     12 
     13 using namespace mozilla::hal;
     14 
     15 namespace mozilla::hal_impl {
     16 
     17 /* The Linux OOM score is a value computed by the kernel ranging between 0 and
     18 * 1000 and indicating how likely is a process to be killed when memory is
     19 * tight. The larger the value the more likely a process is to be killed. The
     20 * score is computed based on the amount of memory used plus an adjustment
     21 * value. We chose our adjustment values to make it likely that processes are
     22 * killed in the following order:
     23 *
     24 * 1. preallocated processes
     25 * 2. background processes
     26 * 3. background processes playing video (but no audio)
     27 * 4. foreground processes or processes playing or recording audio
     28 * 5. gpu process or anything else high priority
     29 * 6. 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 kForegroundHighOomScoreAdjust = 100;
     38 const uint32_t kForegroundOomScoreAdjust = 133;
     39 const uint32_t kBackgroundPerceivableOomScoreAdjust = 167;
     40 const uint32_t kBackgroundOomScoreAdjust = 200;
     41 const uint32_t kPreallocOomScoreAdjust = 233;
     42 
     43 static uint32_t OomScoreAdjForPriority(ProcessPriority aPriority) {
     44  switch (aPriority) {
     45    case PROCESS_PRIORITY_BACKGROUND:
     46      return kBackgroundOomScoreAdjust;
     47    case PROCESS_PRIORITY_BACKGROUND_PERCEIVABLE:
     48      return kBackgroundPerceivableOomScoreAdjust;
     49    case PROCESS_PRIORITY_PREALLOC:
     50      return kPreallocOomScoreAdjust;
     51    case PROCESS_PRIORITY_FOREGROUND:
     52      return kForegroundOomScoreAdjust;
     53    case PROCESS_PRIORITY_FOREGROUND_HIGH:
     54      return kForegroundHighOomScoreAdjust;
     55    default:
     56      return kParentOomScoreAdjust;
     57  }
     58 }
     59 
     60 void SetProcessPriority(int aPid, ProcessPriority aPriority) {
     61  HAL_LOG("LinuxProcessPriority - SetProcessPriority(%d, %s)\n", aPid,
     62          ProcessPriorityToString(aPriority));
     63 
     64  uint32_t oomScoreAdj = OomScoreAdjForPriority(aPriority);
     65 
     66  char path[32] = {};
     67  SprintfLiteral(path, "/proc/%d/oom_score_adj", aPid);
     68 
     69  char oomScoreAdjStr[11] = {};
     70  SprintfLiteral(oomScoreAdjStr, "%d", oomScoreAdj);
     71 
     72  int fd = open(path, O_WRONLY);
     73  if (fd < 0) {
     74    return;
     75  }
     76  const size_t len = strlen(oomScoreAdjStr);
     77  [[maybe_unused]] ssize_t _ = write(fd, oomScoreAdjStr, len);
     78  (void)close(fd);
     79 }
     80 
     81 }  // namespace mozilla::hal_impl