On Tue, Dec 10, 2019 at 09:24:49AM -0700, Jens Axboe wrote: > Seems to me that we have an opportunity to provide something that sits > somewhere in between buffered and O_DIRECT, and this is where > RWF_UNCACHED enters the picture. If this flag is set on IO, we get the > following behavior: > > - If the data is in cache, it remains in cache and the copy (in or out) > is served to/from that. > > - If the data is NOT in cache, we add it while performing the IO. When > the IO is done, we remove it again. > > With this, I can do 100% smooth buffered reads or writes without pushing > the kernel to the state where kswapd is sweating bullets. In fact it > doesn't even register. > > Comments appreciated! Patches are against current git (ish), and can > also be found here: I can't say I particularly like the model, as it still has all the page cache overhead. Direct I/O with bounce buffers for unaligned I/O sounds simpler and faster to me.
