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

[Jesse Barnes]

On Fri, Apr 15, 2022, 4:31 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> 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?

Yes ignore me.

Jesse "returning to his cave of ignorace" Barnes