On Thu, 28 Dec 2023, Greg Kroah-Hartman wrote:
> > I'd argue that the ship on the "sysfs one-value-per-file rule" has sailed
> > for long-standing use cases where either (1) switching is just not
> > possible or (2) switching would be an undue burden to the user.
> >
> > An example of (1) would be THP enablement and defrag options:
> >
> > $ grep . /sys/kernel/mm/transparent_hugepage/{defrag,enabled,shmem_enabled}
> > /sys/kernel/mm/transparent_hugepage/defrag:always defer defer+madvise [madvise] never
> > /sys/kernel/mm/transparent_hugepage/enabled:[always] madvise never
> > /sys/kernel/mm/transparent_hugepage/shmem_enabled:always within_size advise [never] deny force
> >
> > This convention isn't going to change. We're not going to suddenly add a
> > new enablement or defrag option that can only be set in a newly added
> > file that is one-value-per-file.
> >
> > THP was obviously introduced before any sysfs "one-value-per-file rule"
>
> No, the rule has been there since "day one" for sysfs, this file snuck
> in much later with no one noticing it against the "rules" and I've been
> complaining about it every time someone tries to add a new field to it
> that I notice.
>
Ah, gotcha, thanks. I had assumed that the push for one-value-per-file
started after thp, and perhaps even because of thp :) I have to admit
that whenever I log into a new server type one of the first things I do is
$ cat /sys/devices/system/node/node*/distance
and that table just makes intuitive sense. If we were to go back in time
and reimplement that as one-value-per-file, I'd just assume that many
userspace implementations would just need to read 64 different files to
structure it into the same exact table.
On the other hand, I have wished countless times that the thp settings
would have actually been one-value-per-file from the start.
