On Wed, Apr 26, 2017 at 1:38 PM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > Dan Williams <dan.j.williams@xxxxxxxxx> writes: > >> The nvdimm_flush() mechanism helps to reduce the impact of an ADR >> (asynchronous-dimm-refresh) failure. The ADR mechanism handles flushing >> platform WPQ (write-pending-queue) buffers when power is removed. The >> nvdimm_flush() mechanism performs that same function on-demand. >> >> When a pmem namespace is associated with a block device, an >> nvdimm_flush() is triggered with every block-layer REQ_FUA, or REQ_FLUSH >> request. These requests are typically associated with filesystem >> metadata updates. However, when a namespace is in device-dax mode, >> userspace (think database metadata) needs another path to perform the >> same flushing. In other words this is not required to make data >> persistent, but in the case of metadata it allows for a smaller failure >> domain in the unlikely event of an ADR failure. >> >> The new 'flush' attribute is visible when the individual DIMMs backing a >> given interleave-set are described by platform firmware. In ACPI terms >> this is "NVDIMM Region Mapping Structures" and associated "Flush Hint >> Address Structures". Reads return "1" if the region supports triggering >> WPQ flushes on all DIMMs. Reads return "0" the flush operation is a >> platform nop, and in that case the attribute is read-only. > > I can make peace with exposing this to userspace, though I am mostly > against its use. However, sysfs feels like the wrong interface. > Believe it or not, I'd rather see this implemented as an ioctl. > > This isn't a NACK, it's me giving my opinion. Do with it what you will. I hate ioctls with a burning passion so I can't get on board with that change, but perhaps the sentiment behind it is that this is too visible and too attractive being called "flush" in sysfs? Would a name more specific to the mechanism make it more palatable? Like "flush_hint_trigger" or "wpq_drain"? -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
