On Thu 27-07-23 21:30:01, Roman Gushchin wrote: > On Thu, Jul 27, 2023 at 10:15:16AM +0200, Michal Hocko wrote: > > On Thu 27-07-23 15:36:27, Chuyi Zhou wrote: > > > This patchset tries to add a new bpf prog type and use it to select > > > a victim memcg when global OOM is invoked. The mainly motivation is > > > the need to customizable OOM victim selection functionality so that > > > we can protect more important app from OOM killer. > > > > This is rather modest to give an idea how the whole thing is supposed to > > work. I have looked through patches very quickly but there is no overall > > design described anywhere either. > > > > Please could you give us a high level design description and reasoning > > why certain decisions have been made? e.g. why is this limited to the > > global oom sitation, why is the BPF program forced to operate on memcgs > > as entities etc... > > Also it would be very helpful to call out limitations of the BPF > > program, if there are any. > > One thing I realized recently: we don't have to make a victim selection > during the OOM, we [almost always] can do it in advance. > > Kernel OOM's must guarantee the forward progress under heavy memory pressure > and it creates a lot of limitations on what can and what can't be done in > these circumstances. > > But in practice most policies except maybe those which aim to catch very fast > memory spikes rely on things which are fairly static: a logical importance of > several workloads in comparison to some other workloads, "age", memory footprint > etc. > > So I wonder if the right path is to create a kernel interface which allows > to define a OOM victim (maybe several victims, also depending on if it's > a global or a memcg oom) and update it periodically from an userspace. We already have that interface. Just echo OOM_SCORE_ADJ_MAX to any tasks that are to be killed with a priority... Not a great interface but still something available. > In fact, the second part is already implemented by tools like oomd, systemd-oomd etc. > Someone might say that the first part is also implemented by the oom_score > interface, but I don't think it's an example of a convenient interface. > It's also not a memcg-level interface. What do you mean by not memcg-level interface? What kind of interface would you propose instead? > Just some thoughts. > > Thanks! -- Michal Hocko SUSE Labs
