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. 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. -- Chuck Lever
