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

From: Dave Hansen
Date: Thu Sep 10 2020 - 16:58:58 EST

On 9/10/20 3:20 AM, David Hildenbrand wrote:
> 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?
> 2. Restrict it to s390x only. It always returned 0 on other
> architectures, I was not able to find any user.

By "restrict it", do you mean just remove the sysfs file on everything
other than s390x? That seems like a good idea, especially if we don't
have any users. That, plus boot option or something to reenable it
would be nice if someone trips over it disappearing.

If there is a user, we stand a chance of finding them because they'll
hopefully get a good error message. Worst case, an strace will show an
-ENOENT and should be pretty easy to track down.