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Date: Tue, 12 Mar 2019 09:05:32 +0100 From: Michal Hocko <mhocko@...nel.org> To: Suren Baghdasaryan <surenb@...gle.com> Cc: Sultan Alsawaf <sultan@...neltoast.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, Joel Fernandes <joel@...lfernandes.org>, Christian Brauner <christian@...uner.io>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>, devel@...verdev.osuosl.org, linux-mm <linux-mm@...ck.org>, Tim Murray <timmurray@...gle.com> Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android On Mon 11-03-19 15:15:35, Suren Baghdasaryan wrote: > On Mon, Mar 11, 2019 at 1:46 PM Sultan Alsawaf <sultan@...neltoast.com> wrote: > > > > On Mon, Mar 11, 2019 at 01:10:36PM -0700, Suren Baghdasaryan wrote: > > > The idea seems interesting although I need to think about this a bit > > > more. Killing processes based on failed page allocation might backfire > > > during transient spikes in memory usage. > > > > This issue could be alleviated if tasks could be killed and have their pages > > reaped faster. Currently, Linux takes a _very_ long time to free a task's memory > > after an initial privileged SIGKILL is sent to a task, even with the task's > > priority being set to the highest possible (so unwanted scheduler preemption > > starving dying tasks of CPU time is not the issue at play here). I've > > frequently measured the difference in time between when a SIGKILL is sent for a > > task and when free_task() is called for that task to be hundreds of > > milliseconds, which is incredibly long. AFAIK, this is a problem that LMKD > > suffers from as well, and perhaps any OOM killer implementation in Linux, since > > you cannot evaluate effect you've had on memory pressure by killing a process > > for at least several tens of milliseconds. > > Yeah, killing speed is a well-known problem which we are considering > in LMKD. For example the recent LMKD change to assign process being > killed to a cpuset cgroup containing big cores cuts the kill time > considerably. This is not ideal and we are thinking about better ways > to expedite the cleanup process. If you design is relies on the speed of killing then it is fundamentally flawed AFAICT. You cannot assume anything about how quickly a task dies. It might be blocked in an uninterruptible sleep or performin an operation which takes some time. Sure, oom_reaper might help here but still. The only way to control the OOM behavior pro-actively is to throttle allocation speed. We have memcg high limit for that purpose. Along with PSI, I can imagine a reasonably working user space early oom notifications and reasonable acting upon that. -- Michal Hocko SUSE Labs
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