On Thu, Dec 12, 2019 at 7:16 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> I don't know the nocache tool, but I'm guessing it just does the writes
> (or reads) and then uses FADV_DONTNEED to drop behind those pages?
> That's fine for slower use cases, it won't work very well for fast IO.
> The write side currently works pretty much like that internally, whereas
> the read side doesn't use the page cache at all.
Well, I think that if we have this RWF/IOC_UNCACHED flag, maybe we
should make FADV_NOREUSE file descriptors just use it even for regular
read/write..
Right now FADV_NOREUSE is a no-op for the kernel, I think, because we
historically didn't have the facility.
But FADV_DONTNEED is different. That's for dropping pages after use
(ie invalidate_mapping_pages())
Linus
