Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback options

From: John Stoffel
Date: Thu Apr 26 2018 - 15:14:23 EST

>>>>> "James" == James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes:

James> On Wed, 2018-04-25 at 19:00 -0400, Mikulas Patocka wrote:
>> On Wed, 25 Apr 2018, James Bottomley wrote:
>> > > > Do we really need the new config option?  This could just be
>> > > > manually  tunable via fault injection IIUC.
>> > > 
>> > > We do, because we want to enable it in RHEL and Fedora debugging
>> > > kernels, so that it will be tested by the users.
>> > > 
>> > > The users won't use some extra magic kernel options or debugfs
>> files.
>> > 
>> > If it can be enabled via a tunable, then the distro can turn it on
>> > without the user having to do anything.  If you want to present the
>> > user with a different boot option, you can (just have the tunable
>> set
>> > on the command line), but being tunable driven means that you don't
>> > have to choose that option, you could automatically enable it under
>> a
>> > range of circumstances.  I think most sane distributions would want
>> > that flexibility.
>> > 
>> > Kconfig proliferation, conversely, is a bit of a nightmare from
>> both
>> > the user and the tester's point of view, so we're trying to avoid
>> it
>> > unless absolutely necessary.
>> > 
>> > James
>> BTW. even developers who compile their own kernel should have this
>> enabled by a CONFIG option - because if the developer sees the option
>> when browsing through menuconfig, he may enable it. If he doesn't see
>> the option, he won't even know that such an option exists.

James> I may be an atypical developer but I'd rather have a root canal
James> than browse through menuconfig options. The way to get people
James> to learn about new debugging options is to blog about it (or
James> write an article) which google will find the next time
James> I ask it how I debug XXX. Google (probably as a service to
James> humanity) rarely turns up Kconfig options in response to a
James> query.

I agree with James here. Looking at the SLAB vs SLUB Kconfig entries
tells me *nothing* about why I should pick one or the other, as an