On Mon, Jun 16, 2025 at 09:32:16AM -0400, Chuck Lever wrote: > On 6/12/25 12:00 PM, Mike Snitzer wrote: > > On Thu, Jun 12, 2025 at 09:21:35AM -0400, Chuck Lever wrote: > >> On 6/11/25 3:18 PM, Mike Snitzer wrote: > >>> On Wed, Jun 11, 2025 at 10:31:20AM -0400, Chuck Lever wrote: > >>>> On 6/10/25 4:57 PM, Mike Snitzer wrote: > >>>>> Add 'enable-dontcache' to NFSD's debugfs interface so that: Any data > >>>>> read or written by NFSD will either not be cached (thanks to O_DIRECT) > >>>>> or will be removed from the page cache upon completion (DONTCACHE). > >>>> > >>>> I thought we were going to do two switches: One for reads and one for > >>>> writes? I could be misremembering. > >>> > >>> We did discuss the possibility of doing that. Still can-do if that's > >>> what you'd prefer. > >> > >> For our experimental interface, I think having read and write enablement > >> as separate settings is wise, so please do that. > >> > >> One quibble, though: The name "enable_dontcache" might be directly > >> meaningful to you, but I think others might find "enable_dont" to be > >> oxymoronic. And, it ties the setting to a specific kernel technology: > >> RWF_DONTCACHE. > >> > >> So: Can we call these settings "io_cache_read" and "io_cache_write" ? > >> > >> They could each carry multiple settings: > >> > >> 0: Use page cache > >> 1: Use RWF_DONTCACHE > >> 2: Use O_DIRECT > >> > >> You can choose to implement any or all of the above three mechanisms. > > > > I like it, will do for v2. But will have O_DIRECT=1 and RWF_DONTCACHE=2. > > For io_cache_read, either settings 1 and 2 need to set > disable_splice_read, or the io_cache_read setting has to be considered > by nfsd_read_splice_ok() when deciding to use nfsd_iter_read() or > splice read. Yes, I understand. > However, it would be slightly nicer if we could decide whether splice > read can be removed /before/ this series is merged. Can you get NFSD > tested with IOR with disable_splice_read both enabled and disabled (no > direct I/O)? Then we can compare the results to ensure that there is no > negative performance impact for removing the splice read code. I can ask if we have a small window of opportunity to get this tested, will let you know if so.
