Re: [PATCH 1/6] NFSD: add the ability to enable use of RWF_DONTCACHE for all IO

Mike Snitzer
2025-06-12T16:00:36Z

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.

Thanks,
Mike