On Tue 28-11-23 16:34:35, Roman Gushchin wrote: > On Tue, Nov 28, 2023 at 02:23:36PM +0800, Qi Zheng wrote: [...] > > Now I think adding this method might not be a good idea. If we allow > > shrinkers to report thier own private information, OOM logs may become > > cluttered. Most people only care about some general information when > > troubleshooting OOM problem, but not the private information of a > > shrinker. > > I agree with that. > > It seems that the feature is mostly useful for kernel developers and it's easily > achievable by attaching a bpf program to the oom handler. If it requires a bit > of work on the bpf side, we can do that instead, but probably not. And this > solution can potentially provide way more information in a more flexible way. > > So I'm not convinced it's a good idea to make the generic oom handling code > more complicated and fragile for everybody, as well as making oom reports differ > more between kernel versions and configurations. Completely agreed! From my many years of experience of oom reports analysing from production systems I would conclude the following categories - clear runaways (and/or memory leaks) - userspace consumers - either shmem or anonymous memory predominantly consumes the memory, swap is either depleted or not configured. OOM report is usually useful to pinpoint those as we have required counters available - kernel memory consumers - if we are lucky they are using slab allocator and unreclaimable slab is a huge part of the memory consumption. If this is a page allocator user the oom repport only helps to deduce the fact by looking at how much user + slab + page table etc. form. But identifying the root cause is close to impossible without something like page_owner or a crash dump. - misbehaving memory reclaim - minority of issues and the oom report is usually insufficient to drill down to the root cause. If the problem is reproducible then collecting vmstat data can give a much better clue. - high number of slab reclaimable objects or free swap are good indicators. Shrinkers data could be potentially helpful in the slab case but I really have hard time to remember any such situation. On non-production systems the situation is quite different. I can see how it could be very beneficial to add a very specific debugging data for subsystem/shrinker which is developed and could cause the OOM. For that purpose the proposed scheme is rather inflexible AFAICS. -- Michal Hocko SUSE Labs
