On Fri, Nov 08, 2013 at 12:17:37AM -0800, Kent Overstreet wrote: > The core issue isn't whether the IO is going to a block based filesystem > (but thanks for pointing out that that's not necessarily true!) but > whether we want to work with pinned pages or not. If pinned pages are ok > for everything, then bios as a common interface work - likely evolving > them a bit to be more general (it's just bi_bdev and bi_sector that's > actually block specific) - and IMO that would be far preferable to this > abstraction layer. > > If OTOH we need a common interface that's also for places where we can't > afford the overhead of pinning user pages - that's a different story, > and maybe we do need all this infrastructure then. That's why I'm asking > about the stuff you meantioned, I'm honestly not sure. For both of them we will deal with kernel-allocated pages that are never mapped to userspace. This is likely to be true for all the consumers of in-kernel aio/dio as the existing interfaces handle user pages just fine. > What I'm working towards though is a clean separation between buffered > and direct code paths, so that buffered IO can continue work with iovs > and for O_DIRECT the first thing you do is fill out a bio with pinned > pages and send it down to filesystem code or wherever it's going to go. I don't think pushing bios above the fs interface is a good idea. Note that the iovecs come from userspace for the user pages cases, so there is little we can do about that, and non-bio based direct I/O implementations generally work directly at just that level and never even touch the direct-io.c code. If you want to redo the ->direct_IO address_space operation and generic_file_direct_write and the direct I/O side of generic_file_aio_read (both of which aren't anywhere near as generic as the name claims) I'm all for it, but it really won't affect the consumer of the in-kernel aio/dio code. > That make sense? I can show you more concretely what I'm working on if > you want. Or if I'm full of crap and this is useless for what you guys > want I'm sure you'll let me know :) It sounds interesting, but also a little confusing at this point, at least from the non-block side of view. -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
