On Wed, 17 Feb 2016, Xishi Qiu wrote: > Hi David, > > Thanks for your advice. > > I have a stupid question, what's the main difference between lmk and oom?
Hi Xishi, it's not a stupid question at all! Low memory killer appears to be implemented as a generic shrinker that iterates through the tasklist and tries to free memory before the generic oom killer. It has two tunables, "adj" and "minfree": "minfree" describes what class of processes are eligible based on how many free pages are left on the system and "adj" defines that class by using oom_score_adj values. So LMK is trying to free memory before all memory is depleted based on heuristics for systems that load the driver whereas the generic oom killer is called to kill a process when reclaim has failed to free any memory and there's no forward progress. > 1) lmk is called when reclaim memory, and oom is called when alloc failed in > slow path. Yeah, and I don't think LMK provides any sort of guarantee against all memory being fully depleted before it can run, so it would probably be best effort. > 2) lmk has several lowmem thresholds and oom is not. Right, and it abuses oom_score_adj, which is a generic oom killer tunable to define priorities to kill at different levels of memory availability. > 3) others? > LMK also abuses TIF_MEMDIE which is used by the generic oom killer to allow a process to free memory. Since the system is out of memory when it is called, a process often needs additional memory to even exit, so we set TIF_MEMDIE to ignore zone watermarks in the page allocator. LMK should not be using this, there should already be memory available for it to allocate from. To fix these issues with LMK, I think it should: - send SIGKILL to terminate a process in lowmem situations, but not set TIF_MEMDIE and implement its own way of determining when to kill additional processes, and - introduce its own tunable to define the priority of kill when it runs rather than oom_score_adj, which is a proportion of memory to bias against, not a priority at all.
