> On May 15, 2024, at 6:30 AM, Kanchan Joshi <joshiiitr@xxxxxxxxx> wrote: > > On Tue, May 14, 2024 at 1:00 PM Viacheslav Dubeyko <slava@xxxxxxxxxxx> wrote: >>> On May 14, 2024, at 9:47 PM, Kanchan Joshi <joshiiitr@xxxxxxxxx> wrote: >>> >>> On Mon, May 13, 2024 at 2:04 AM Viacheslav Dubeyko <slava@xxxxxxxxxxx> wrote: >>>> >>>> >>>> >>>>> On May 10, 2024, at 4:40 PM, Kanchan Joshi <joshi.k@xxxxxxxxxxx> wrote: >>>>> >>>>> Flexible Data Placement (FDP), as ratified in TP 4146a, allows the host >>>>> to control the placement of logical blocks so as to reduce the SSD WAF. >>>>> >>>>> Userspace can send the data lifetime information using the write hints. >>>>> The SCSI driver (sd) can already pass this information to the SCSI >>>>> devices. This patch does the same for NVMe. >>>>> >>>>> Fetches the placement-identifiers (plids) if the device supports FDP. >>>>> And map the incoming write-hints to plids. >>>>> >>>> >>>> >>>> Great! Thanks for sharing the patch. >>>> >>>> Do we have documentation that explains how, for example, kernel-space >>>> file system can work with block layer to employ FDP? >>> >>> This is primarily for user driven/exposed hints. For file system >>> driven hints, the scheme is really file system specific and therefore, >>> will vary from one to another. >>> F2FS is one (and only at the moment) example. Its 'fs-based' policy >>> can act as a reference for one way to go about it. >> >> Yes, I completely see the point. I would like to employ the FDP in my >> kernel-space file system (SSDFS). And I have a vision how I can do it. >> But I simply would like to see some documentation with the explanation of >> API and limitations of FDP for the case of kernel-space file systems. > > Nothing complicated for early experimentation. > Once FS has determined the hint value, it can put that into > bio->bi_write_hint and send bio down. > > If SSDFS cares about user-exposed hints too, it can choose different > hint values than what is exposed to user-space. > Or it can do what F2FS does - use the mount option as a toggle to > reuse the same values either for user-hints or fs-defined hints. How many hint values file system can use? Any limitations here? And how file system can detect that it’s FDP-based device? Thanks, Slava.
