On Fri, Nov 21, 2014 at 02:06:57AM -0800, Christoph Hellwig wrote: > On Tue, Nov 18, 2014 at 11:22:35PM -0800, Omar Sandoval wrote: > > Here's a nice little bit of insanity I put together in that direction -- > > consider it a discussion point more than a patch. It does two things: > > > > - Uses an ITER_BVEC iov_iter to do direct_IO for swap_readpage. This makes > > swap_readpage a synchronous operation, but I think that's the best we can > > do > > with the existing interface. > > Note that ->read_iter for direct-io supports async I/O in general. By > resurrecting some of the older attempts to do in-kernel aio this could > be made async easily. > > > - Unless I'm missing something, there don't appear to be any instances of > > ITER_BVEC | READ in the kernel, so the dio path doesn't know not to dirty > > pages it gets that way. Dave Kleikamp and Ming Lei each previously > > submitted > > patches doing this as part of adding an aio_kernel interface. (The NFS > > direct > > I/O implementation doesn't know how to deal with these either, so this > > patch > > actually breaks the only existing user of this code path, but in the > > interest > > of keeping the patch short, I didn't try to fix it :) > > Right, we'd need to look into. Bonus points of allowing this as a zero > copy read. > > > Btw, in the long run I would much prefer killing of the current horrible > swap using bmap path in favor of an enhanced direct I/O path. Looks like I just raced on your email and sent a v2 of my patch series before seeing this response :) I'll take a closer look at this tomorrow, thanks for getting back to me.
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