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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at */
#include "Hal.h"
#include "HalLog.h"
#include "mozilla/Sprintf.h"
#include "mozilla/Unused.h"
#include <fcntl.h>
#include <unistd.h>
using namespace mozilla::hal;
namespace mozilla::hal_impl {
/* The Linux OOM score is a value computed by the kernel ranging between 0 and
* 1000 and indicating how likely is a process to be killed when memory is
* tight. The larger the value the more likely a process is to be killed. The
* score is computed based on the amount of memory used plus an adjustment
* value. We chose our adjustment values to make it likely that processes are
* killed in the following order:
* 1. preallocated processes
* 2. background processes
* 3. background processes playing video (but no audio)
* 4. foreground processes or processes playing or recording audio
* 5. the parent process
* At the time of writing (2022) the base score for a process consuming very
* little memory seems to be around ~667. Our adjustments are thus designed
* to ensure this order starting from a 667 baseline but trying not to go too
* close to the 1000 limit where they would be clamped. */
const uint32_t kParentOomScoreAdjust = 0;
const uint32_t kForegroundOomScoreAdjust = 100;
const uint32_t kBackgroundPerceivableOomScoreAdjust = 133;
const uint32_t kBackgroundOomScoreAdjust = 167;
const uint32_t kPreallocOomScoreAdjust = 233;
static uint32_t OomScoreAdjForPriority(ProcessPriority aPriority) {
switch (aPriority) {
return kBackgroundOomScoreAdjust;
return kBackgroundPerceivableOomScoreAdjust;
return kPreallocOomScoreAdjust;
return kForegroundOomScoreAdjust;
return kParentOomScoreAdjust;
void SetProcessPriority(int aPid, ProcessPriority aPriority) {
HAL_LOG("LinuxProcessPriority - SetProcessPriority(%d, %s)\n", aPid,
uint32_t oomScoreAdj = OomScoreAdjForPriority(aPriority);
char path[32] = {};
SprintfLiteral(path, "/proc/%d/oom_score_adj", aPid);
char oomScoreAdjStr[11] = {};
SprintfLiteral(oomScoreAdjStr, "%d", oomScoreAdj);
int fd = open(path, O_WRONLY);
if (fd < 0) {
const size_t len = strlen(oomScoreAdjStr);
Unused << write(fd, oomScoreAdjStr, len);
Unused << close(fd);
} // namespace mozilla::hal_impl