Re: + mm-shuffle-default-enable-all-shuffling.patch added to -mm tree

[Michal Hocko <mhocko@kernel.org>]

On Tue 12-02-19 13:46:22, Andrew Morton wrote:
> On Tue, 12 Feb 2019 09:54:28 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> 
> > On Wed 06-02-19 12:02:54, Andrew Morton wrote:
> > > From: Dan Williams <dan.j.williams@intel.com>
> > > Subject: mm/shuffle: default enable all shuffling
> > > 
> > > Per Andrew's request arrange for all memory allocation shuffling code to
> > > be enabled by default.
> > > 
> > > The page_alloc.shuffle command line parameter can still be used to disable
> > > shuffling at boot, but the kernel will default enable the shuffling if the
> > > command line option is not specified.
> > > 
> > > Link: http://lkml.kernel.org/r/154943713572.3858443.11206307988382889377.stgit@dwillia2-desk3.amr.corp.intel.com
> > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > > Cc: Kees Cook <keescook@chromium.org>
> > > Cc: Michal Hocko <mhocko@suse.com>
> > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > Cc: Keith Busch <keith.busch@intel.com>
> > > 
> > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > 
> > I hope this is mmotm only thing and even then, is this really
> > something we want for linux-next? There are people doing testing and
> > potentially performance testing on that tree. Do we want to invalidate
> > all that work? I can see some argument about a testing coverage but do
> > we really need it for the change like this? The randomization is quite
> > simple to review and I assume Dan has given this good testing before
> > submition.
> 
> Please see the mailing list discussion.  Without this patch the feature
> is likely to end up in mainline with next to no testing other than Dan's.

Isn't that the case for most of the functionality behind CONFIG_$FOO
that doesn't get enabled by default?

It is not that I care too much but I find this way of argumentation
strange. It is the submitter to make sure the feature is tested properly
and reviewers should make sure the overall design and implementation
makes sense. I do not see reason why all users of linux-next should be a
guinea pigs without knowing that.
-- 
Michal Hocko
SUSE Labs