Re: [page-reclaim] Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks

[Matthew Wilcox]

On Fri, Apr 15, 2022 at 04:24:14PM -0700, Jesse Barnes wrote:
> On Fri, Apr 15, 2022 at 4:04 PM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > And for ordinary users, a WARN_ON_ONCE() is about a million times
> > better, becasue:
> >
> >  - the machine will hopefully continue working, so they can report the warning
> >
> >  - even when they don't notice them, distros tend to have automated
> > reporting infrastructure
> >
> > That's why I absolutely *DETEST* those stupid BUG_ON() cases - they
> > will often kill the machine with nasty locks held, resulting in a
> > completely undebuggable thing that never gets reported.
> >
> > Yes, you can be careful and only put BUG_ON() in places where recovery
> > is possible. But even then, they have no actual _advantages_ over just
> > a WARN_ON_ONCE.
> 
> Generally agreed, and not to belabor this relatively small issue, but in some
> environments like cloud or managed client deployments, a crash can actually
> be preferable so we can get a dump, reboot the machine, and get things going
> again for the application or user, then debug offline.  So having the
> flexibility to
> do that in those situations is helpful.  And there, a full crash dump is better
> than just a log report with the WARN info, since debugging may be easier with
> all the kernel memory.

But for those situations, don't you set panic_on_warn anyway?