Re: Ways to deprecate /sys/devices/system/memory/memoryX/phys_device ?

On Fri, Sep 25, 2020 at 04:49:28PM +0200, David Hildenbrand wrote:

quoted

quoted

There were once RFC patches to make use of it in ACPI, but it could be
solved using different interfaces [1].


While I'd love to rip it out completely, I think it would break old
lsmem/chmem completely - and I assume that's not acceptable. I was
wondering what would be considered safe to do now/in the future:

1. Make it always return 0 (just as if "sclp.rzm" would be set to 0 on
s390x). This will make old lsmem/chmem behave differently after
switching to a new kernel, like if sclp.rzm would not be set by HW -
AFAIU, it will assume all memory is in a single memory increment. Do we
care?

No, at least not until that kernel change would be backported to some
old distribution level where we still use lsmem/chmem from s390-tools.
Given that this is just some clean-up w/o any functional benefit, and
hopefully w/o any negative impact, I think we can safely assume that no
distributor will do that "just for fun".

Even if there would be good reasons for backports, then I guess we also
have good reasons for backporting / switching to the util-linux version
of lsmem / chmem for such distribution levels. Alternatively, adjust the
s390-tools lsmem / chmem there.

But I would rather "rip it out completely" than just return 0. You'd
need some lsmem / chmem changes anyway, at least in case this would
ever be backported.

Thanks for your input Gerald.

So unless people would be running shiny new kernels on older
distributions it shouldn't be a problem (and I don't think we care too
much about something like that). I don't expect something like that to
get backported - there is absolutely no reason to do so IMHO.

We do care about this, Andrew used to have an old Fedora 9 box or
something like that, that he tourtured many of us with bug reports when
we broke it :)

So watch out, people keep old userspace around for much longer than you
can possibly imagine because they don't like having their use-cases in
userspace change, and we have made the guarantee to them that they _CAN_
trust us to not break things in userspace.

It's a slow age-out, but watch out, you might have to revert things...

good luck!

greg k-h