On 2022/04/23 10:25, Roman Gushchin wrote: >>> I agree. However the OOM killer _has_ to make the progress even in such rare >>> circumstances. >> >> Oh, and the concern is allocator recursion? Yeah, that's a good point. > > Yes, but not the only problem. > >> >> Do you know if using memalloc_noreclaim_(save|restore) is sufficient for that, >> or do we want GFP_ATOMIC? I'm already using GFP_ATOMIC for allocations when we >> generate the report on slabs, since we're taking the slab mutex there. > > And this is another problem: grabbing _any_ locks from the oom context is asking > for trouble: you can potentially enter the oom path doing any allocation, so > now you have to check that no allocations are ever made holding this lock. > And I'm not aware of any reasonable way to test it, so most likely it ends up > introducing some very subtle bags, which will be triggered once a year. > You can't allocate memory nor hold locks from OOM context. Since oom_lock mutex serializes OOM reporting, you could use statically pre-allocated buffer for holding one line of output. Correlating whole report will be done by the userspace program with the aid of CONFIG_PRINTK_CALLER=y.
