linux: use -1000 adjustment for /proc/<pid>/oom_score_adj first #15
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The intent of the bcd_os_oom_adjust() function is apparently to disable OOM killing of the process, as it writes the value -17 to the /proc/<pid>/oom_adj path if it exists. Per the kernel documentation: "For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also be used to tune the badness score. Its acceptable values range from -16 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 (OOM_DISABLE) to disable oom killing entirely for that task." If /proc/<pid>/oom_adj does not exist, bcd_os_oom_adjust() attempts to write the same value (-17) to /proc/<pid>/oom_score_adj. This results in different behavior, because this value is within the OOM score adjustment range. Per the kernel documentation: "The value of /proc/<pid>/oom_score_adj is added to the badness score before it is used to determine which task to kill. Acceptable values range from -1000 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to polarize the preference for oom killing either by always preferring a certain task or completely disabling it. The lowest possible value, -1000, is equivalent to disabling oom killing entirely for that task since it will always report a badness score of 0." Additionally, the bcd_os_oom_adjust() function attempts to write to /proc/<pid>/oom_adj and, if that path does not exist, falls back to writing to /proc/<pid>/oom_score_adj. On modern kernels where both paths exist, this results in a kernel warning being logged: https://github.com/torvalds/linux/blob/f69d02e37a85645aa90d18cacfff36dba370f797/fs/proc/base.c#L1074-L1080 This commit updates bcd_os_oom_adjust() to write "-1000" to /proc/<pid>/oom_score_adj first and, if that path does not exist, "-17" to the legacy /proc/<pid>/oom_adj path.
thatsafunnyname
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Feb 9, 2024
Avoid overflow on "score" read buffer when set to "-17", when "write" is called. Introduced in backtrace-labs@e5740aa from backtrace-labs#15
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The intent of the
bcd_os_oom_adjust()function is apparently to disable OOM killing of the process, as it writes the value -17 to the/proc/<pid>/oom_adjpath if it exists.Per the kernel documentation:
If
/proc/<pid>/oom_adjdoes not exist,bcd_os_oom_adjust()attempts to write the same value (-17) to/proc/<pid>/oom_score_adj. This results in different behavior, because this value is within the OOM score adjustment range. Per the kernel documentation:Additionally, the
bcd_os_oom_adjust()function attempts to write to/proc/<pid>/oom_adjand, if that path does not exist, falls back to writing to/proc/<pid>/oom_score_adj. On modern kernels where both paths exist, this results in a kernel warning being logged:https://github.com/torvalds/linux/blob/f69d02e37a85645aa90d18cacfff36dba370f797/fs/proc/base.c#L1074-L1080
This commit updates
bcd_os_oom_adjust()to write "-1000" to/proc/<pid>/oom_score_adjfirst and, if that path does not exist, "-17" to the legacy/proc/<pid>/oom_adjpath.