On 6/19/25 4:19 PM, Mike Snitzer wrote: > On Tue, Jun 17, 2025 at 01:31:23PM -0400, Chuck Lever wrote: >> On 6/17/25 1:22 PM, Mike Snitzer wrote: >>> On Mon, Jun 16, 2025 at 12:10:38PM -0400, Mike Snitzer wrote: >>>> 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. >>>> >>> >>> I was able to enlist the help of Keith (cc'd) to get some runs in to >>> compare splice_read vs vectored read. A picture is worth 1000 words: >>> https://original.art/NFSD_splice_vs_buffered_read_IOR_EASY.jpg >>> >>> Left side is with splice_read running IOR_EASY with 48, 64, 96 PPN >>> (Processes Per Node on each client) respectively. Then the same >>> IOR_EASY workload progression for buffered IO on the right side. >>> >>> 6x servers with 1TB memory and 48 cpus, each configured with 32 NFSD >>> threads, with CPU pinning and 4M Read Ahead. 6x clients running IOR_EASY. >>> >>> This was Keith's take on splice_read's benefits: >>> - Is overall faster than buffered at any PPN. >>> - Is able to scale higher with PPN (whereas buffered is flat). >>> - Safe to say splice_read allows NFSD to do more IO then standard >>> buffered. >> >> I thank you and Keith for the data! > > You're welcome. > >>> (These results came _after_ I did the patch to remove all the >>> splice_read related code from NFSD and SUNRPC.. while cathartic, alas >>> it seems it isn't meant to be at this point. I'll let you do the >>> honors in the future if/when you deem splice_read worthy of removal.) >> >> If we were to make all NFS READ operations use O_DIRECT, then of course >> NFSD's splice read should be removed at that point. > > Yes, that makes sense. I still need to try Christoph's idea (hope to > do so over next 24hrs): > https://lore.kernel.org/linux-nfs/aEu3o9imaQQF9vyg@xxxxxxxxxxxxx/ > > But for now, here is my latest NFSD O_DIRECT/DONTCACHE work, think of > the top 6 commits as a preview of what'll be v2 of this series: > https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/log/?h=kernel-6.12.24/nfsd-testing I was waiting for a series repost, but in the meantime... The one thing that caught my eye was the relocation of fh_getattr(). - If fh_getattr() is to be moved to fs/nfsd/vfs.c, then it should be renamed nfsd_getattr() (or similar) to match the API naming convention in that file. - If fh_getattr() is to keep its current name, then it should be moved to where the other fh_yada() functions reside, in fs/nfsd/nfsfh.c In a private tree, I constructed a patch to do the latter. I can post that for comment. -- Chuck Lever
