Re: [PATCH 00/10] OOM Debug print selection and additional information

Qian Cai
2019-08-28T00:50:04Z

> On Aug 27, 2019, at 8:23 PM, Edward Chron <echron@arista.com> wrote:
>
>
>
> On Tue, Aug 27, 2019 at 5:40 AM Qian Cai <cai@lca.pw> wrote:
> On Mon, 2019-08-26 at 12:36 -0700, Edward Chron wrote:
> > This patch series provides code that works as a debug option through
> > debugfs to provide additional controls to limit how much information
> > gets printed when an OOM event occurs and or optionally print additional
> > information about slab usage, vmalloc allocations, user process memory
> > usage, the number of processes / tasks and some summary information
> > about these tasks (number runable, i/o wait), system information
> > (#CPUs, Kernel Version and other useful state of the system),
> > ARP and ND Cache entry information.
> >
> > Linux OOM can optionally provide a lot of information, what's missing?
> > ----------------------------------------------------------------------
> > Linux provides a variety of detailed information when an OOM event occurs
> > but has limited options to control how much output is produced. The
> > system related information is produced unconditionally and limited per
> > user process information is produced as a default enabled option. The
> > per user process information may be disabled.
> >
> > Slab usage information was recently added and is output only if slab
> > usage exceeds user memory usage.
> >
> > Many OOM events are due to user application memory usage sometimes in
> > combination with the use of kernel resource usage that exceeds what is
> > expected memory usage. Detailed information about how memory was being
> > used when the event occurred may be required to identify the root cause
> > of the OOM event.
> >
> > However, some environments are very large and printing all of the
> > information about processes, slabs and or vmalloc allocations may
> > not be feasible. For other environments printing as much information
> > about these as possible may be needed to root cause OOM events.
> >
>
> For more in-depth analysis of OOM events, people could use kdump to save a
> vmcore by setting "panic_on_oom", and then use the crash utility to analysis the
> vmcore which contains pretty much all the information you need.
>
> Certainly, this is the ideal. A full system dump would give you the maximum amount of
> information.
>
> Unfortunately some environments may lack space to store the dump,

Kdump usually also support dumping to a remote target via NFS, SSH etc

> let alone the time to dump the storage contents and restart the system. Some

There is also “makedumpfile” that could compress and filter unwanted memory to reduce
the vmcore size and speed up the dumping process by utilizing multi-threads.

> systems can take many minutes to fully boot up, to reset and reinitialize all the
> devices. So unfortunately this is not always an option, and we need an OOM Report.

I am not sure how the system needs some minutes to reboot would be relevant for the
discussion here. The idea is to save a vmcore and it can be analyzed offline even on
another system as long as it having a matching “vmlinux.".