On Thu, 14 Dec 2023, Pasha Tatashin wrote: > > > Whenever a new fields are added one of the following: node_stat_item > > > numa_stat_item zone_stat_item, the /sys/devices/system/node/nodeX/vmstat > > > files are auto expanded. > > > > > > This is a problem, as sysfs files should be only one value per file. > > > > Does this patch address the one-value-per-file issue? (I think that ship > > has sailed for vmstat.) > > That ship has sailed for vmstat, this patch addresses what was asked > by GregKH: not to add new values to vmstat, as not to make the > existing problem even worse. The sysfs file system has a one page > limit per file. The developers will decide how to export the new items > added to node_stat, numa_stat, zone_stat individually. Each new item > can be exported in its own files, and must have its own documentation > about interface stability, value meaning, and expectations when the > stat file is absent. > As of at least 6.5, /proc/vmstat is a strict superset of the per-node vmstat. Why is that a problem? There's great benefit to being able to use the sample implementations to parse either /proc/vmstat *or* the per-node vmstat and without needing to read the per-node vmstat plus some new set of sysfs files that are one-value-per-file. The per-node vmstat will always be multiple values, in fact it's a key value pair. I have to think that doing anything else for vmstat is just adding complexity (like this patch) and actually making it *harder* on userspace to read the data it needs. Yes, the per-node vmstat likely shouldn't be in sysfs at all but it appears to have been added there 13+ years ago because it was a convenient place to add a per-node variant. That's not ideal, but owell.
