On 4/23/25 11:22 AM, Matthew Wilcox wrote: > On Wed, Apr 23, 2025 at 10:38:37AM -0400, Chuck Lever wrote: >> On 4/23/25 12:25 AM, trondmy@xxxxxxxxxx wrote: >>> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> >>> >>> The following patch set attempts to add support for the RWF_DONTCACHE >>> flag in preadv2() and pwritev2() on NFS filesystems. >> >> Hi Trond- >> >> "RFC" in the subject field noted. >> >> The cover letter does not explain why one would want this facility, nor >> does it quantify the performance implications. >> >> I can understand not wanting to cache on an NFS server, but don't you >> want to maintain a data cache as close to applications as possible? > > If you look at the original work for RWF_DONTCACHE, you'll see this is > the application providing the hint that it's doing a streaming access. > It's only applied to folios which are created as a result of this > access, and other accesses to these folios while the folios are in use > clear the flag. So it's kind of like O_DIRECT access, except that it > does go through the page cache so there's none of this funky alignment > requirement on the userspace buffers. OK, was wondering whether this behavior was opt-in; sounds like it is. Thanks for setting me straight. -- Chuck Lever
