To detect lmkd being stuck on a syscall for prolonged period of time,
introduce a watchdog thread which gets set when lmkd starts handling of
events and is reset after handling is done. If it takes more than the
timeout period (2 sec) to handle an event, watchdog wakes up and kills
the least important process to prevent mounting memory pressure caused
by lmkd lockup. After a kill, watchdog will wait for the reset for
another timeout period and kill again. This repeats until lmkd unlocks
and resets the watchdog.
Bug: 201671997
Test: induce random sleep in lmkd main handler and observe watchdog kills
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I56a55834582e11c06cc6cf9da3bc7380e634b301
process_mrelease syscall can be used to expedite memory release of
a process after it was killed. This allows memory to be released
without the target process being scheduled, therefore does not depend
on target's priority or the CPU it's running on.
However process_mrelease syscall can take considerable time. Blocking
lmkd main thread during that time can cause memory pressure events
being missed while lmkd is busy reaping previous target's memory.
For this reason reaping should be done in a separate thread. This way
lmkd main thread can keep monitoring memory pressure while memory is
being released.
Introduce Reaper class which maintains a pool of threads to perform
process killing and reaping. The main thread submits a request to the
Reaper to kill and reap the process without blocking. If all the threads
in the pool are busy at the time the next kill is needed, the kill is
performed by the main thread without reaping.
Bug: 130172058
Bug: 189803002
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: If7b10fdd1838bdfeea3fed3031565feffe0b52be
Suren Baghdasaryan