Re: Major regression on hackbench with SLUB (more numbers)

Ingo Molnar
2007-12-22T19:30:36Z

* Ingo Molnar <mingo@elte.hu> wrote:

> I'd also not rely on the fact that only a few people are complaining.
> Most people, even 2.6.24-rc early adopters, still use SLAB because
> early adopters typically use their .23 .config and do a 'make
> oldconfig' - which picks up SLAB. So SLUB use will become more
> widespread only once 2.6.24 is out and is packaged in distros. Distros
> will likely pick SLUB if there's no performance worries and if it's
> the default. Fedora rawhide already uses SLUB.

here's some silly statistics about allocator coverage on lkml, based on
configs reported to lkml in the past 4 months:

$ for N in SLAB SLUB SLOB; do printf "%s: " $N; grep ^CONFIG_$N=y linux-kernel | wc -l; done
SLAB: 70
SLUB: 77
SLOB: 4

so SLUB and SLAB is utilized about equally amongst people who reported
configs to lkml.

But people who use SLUB enabled it intentionally - and they are thus
much less likely to complain about this choice of them.

Reporting:

"I just enabled SLUB instead of SLAB, and hey guys, it does not have
SLABinfo"

has a foolish ring to it, doesnt it? I'd rather ask carefully, like this
person did:

http://kerneltrap.org/mailarchive/linux-kernel/2007/10/12/335765

This is one of the reasons why i think the whole SLAB->SLUB renaming was
bad - we should have done SLAB2 or SLAB^2 instead, so that people expect
_at least as good_ behavior (performance, features, etc.) from SLUB as
from SLAB. Instead of "something different".

anyway ... i think we still generally suck _alot_ at providing
near-transparent kernel upgrades to users. (kernel upgrades are still a
pain and risk, and often just due to poor developer choices on our
side.)

It's nowhere near as bad as the 2.4->2.6 transition was (in fact it
shouldnt even be mentioned in the same sentence), and it's getting
better gradually, but i think we should just by default be 10 times more
careful about these things - whenever it is borderline technically sane
to do so. We induce enough unintentional breakage of user-space, we
shouldnt compound it with intentional breakages. The kernel community
still has _a lot_ of user and distro trust to win back. So being seen as
over-cautious wont harm.

Ingo