On Wed, Dec 20, 2017 at 01:16:49PM -0800, Matthew Wilcox wrote: > On Wed, Dec 20, 2017 at 12:22:21PM -0800, Dave Hansen wrote: > > On 12/20/2017 10:19 AM, Matthew Wilcox wrote: > > > I don't know what the right interface is, but my laptop has a set of > > > /sys/devices/system/memory/memoryN/ directories. Perhaps this is the > > > right place to expose write_bw (etc). > > > > Those directories are already too redundant and wasteful. I think we'd > > really rather not add to them. In addition, it's technically possible > > to have a memory section span NUMA nodes and have different performance > > properties, which make it impossible to represent there. > > > > In any case, ACPI PXM's (Proximity Domains) are guaranteed to have > > uniform performance properties in the HMAT, and we just so happen to > > always create one NUMA node per PXM. So, NUMA nodes really are a good fit. > > I think you're missing my larger point which is that I don't think this > should be exposed to userspace as an ACPI feature. Because if you do, > then it'll also be exposed to userspace as an openfirmware feature. > And sooner or later a devicetree feature. And then writing a portable > program becomes an exercise in suffering. > > So, what's the right place in sysfs that isn't tied to ACPI? A new > directory or set of directories under /sys/devices/system/memory/ ? Oh, the current location isn't at all tied to acpi except that it happens to be named 'hmat'. When it was all named 'hmem' it was just: /sys/devices/system/hmem Which has no ACPI-isms at all. I'm happy to move it under /sys/devices/system/memory/hmat if that's helpful, but I think we still have the issue that the data represented therein is still pulled right from the HMAT, and I don't know how to abstract it into something more platform agnostic until I know what data is provided by those other platforms. For example, the HMAT provides latency information and bandwidth information for both reads and writes. Will the devicetree/openfirmware/etc version have this same info, or will it be just different enough that it won't translate into whatever I choose to stick in sysfs? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
