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