On Sun, Nov 10, 2024 at 08:27:52AM -0700, Jens Axboe wrote: > 5 years ago I posted patches adding support for RWF_UNCACHED, as a way > to do buffered IO that isn't page cache persistent. The approach back > then was to have private pages for IO, and then get rid of them once IO > was done. But that then runs into all the issues that O_DIRECT has, in > terms of synchronizing with the page cache. Today's a holiday, and I suspect you're going to do a v3 before I have a chance to do a proper review of this version of the series. I think "uncached" isn't quite the right word. Perhaps 'RWF_STREAMING' so that userspace is indicating that this is a streaming I/O and the kernel gets to choose what to do with that information. Also, do we want to fail I/Os to filesystems which don't support it? I suppose really sophisticated userspace might fall back to madvise(DONTNEED), but isn't most userspace going to just clear the flag and retry the I/O? Um. Now I've looked, we also have posix_fadvise(POSIX_FADV_NOREUSE), which is currently a noop. But would we be better off honouring POSIX_FADV_NOREUSE than introducing RWF_UNCACHED? I'll think about this some more while I'm offline.
