Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.

Mel Gorman
2020-10-02T10:19:58Z

On Fri, Oct 02, 2020 at 11:58:58AM +0200, Peter Zijlstra wrote:
> > It's enabled by default by enough distros that adding too many checks
> > is potentially painful. Granted it would be missed by most benchmarking
> > which tend to control allocations from userspace but a lot of performance
> > problems I see are the "death by a thousand cuts" variety.
>
> Oh quite agreed, aka death by accounting. But if people are enabling
> DEBUG options in production kernels, there's something wrong, no?
>

You'd think but historically I believe DEBUG_VM was enabled for some
distributions because it made certain classes of problems easier to debug
early. There is also a recent trend for enabling various DEBUG options for
"hardening" even when they protect very specific corner cases or are for
intended for kernel development. I've pushed back where I have an opinion
that matters but it's generally corrosive.

> Should we now go add CONFIG_REALLY_DEBUG_STAY_AWAY_ALREADY options?

It's heading in that direction :(

--
Mel Gorman
SUSE Labs