On Sun, Dec 24, 2023 at 4:26 PM David Rientjes <rientjes@xxxxxxxxxx> wrote: > > 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? The intent of this series is to stop auto expanding /sys/devices/system/node/nodeX/vmstat as sysfs should only be one value per file, and the task is not to make things worse. /proc/vmstat is mostly ok, however we might not need to auto expand it as well, to avoid situations where removing a field becomes a problem, and we have to keep it in the file forever, like what we do with nr_unstable. > 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. Yes, but that file is already large, and soon can overflow a page size, instead of converting it to a binary format, let's add new items as one item per-file. > 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. It is up-to GregKH who requested this change. Greg, specifically requested not to add new fields into per-node vmstat, and we are adding new fields with per-page metadata series, and IOMMU accounting series as these files are auto-expanded without this series. Pasha
