On 08/21/2013 11:39 AM, Benjamin LaHaise wrote: > On Wed, Aug 21, 2013 at 11:30:22AM -0500, Dave Kleikamp wrote: >> Ben, >> First, let me apologize for neglecting to copy you and linux-aio on the >> applicable patches. I've been carrying along this patchset, assuming I >> had gotten the proper cc's correct a while back, but I somehow missed >> the aio pieces. > > Thanks. Let's figure out how to tackle this best. > >> On 08/21/2013 08:02 AM, Benjamin LaHaise wrote: > ... >>> First off, have you tested that this series actually works when merged with >>> the pending AIO changes from Kent? There a git tree with those pending >>> changes at git://git.kvack.org/~bcrl/aio-next.git , and they're in >>> linux-next. >> >> I've lightly tested the patchset against the linux-next tree, running a >> fio job on loop-mounted filesystems of different fs types. > > Good to hear. >> >>> One of the major problems your changeset continues to carry is that your >>> new read_iter/write_iter operations permit blocking (implicitely), which >>> really isn't what we want for aio. If you're going to introduce a new api, >>> it should be made non-blocking, and enforce that non-blocking requirement >>> (ie warn when read_iter/write_iter methods perform blockin operations, >>> similar to the warnings when scheduling in atomic mode). This means more >>> changes for some filesystem code involved, something that people have been >>> avoiding for years, but which really needs to be done. >> >> I'm not really sure how the read_iter and write_iter operations are more >> likely to block than the current aio_read and aio_write operations. Am I >> missing something? > > What you say is true, however, my point is more that it will be far easier > to fix this issue by making it a hard constraint of a new API than it is > to do a system-wide retrofit. You're converting code over to use the new > API one by one, so adding a little bit more work to try and finally sort > out this issue while making those conversions would be vrey helpful. > > I'm not saying that you should be required to write the code to cope with > this additional requirement (I'm perfectly happy to help with that, and > can probably get some time for that at $work), but more that if we're > going to be changing all of the filesystems, we might as well try to get > things right. I don't really intend to make the patchset any more complicated than it already is. The read/write_iter operations are intended to be as near a replacement as possible to aio_read/write with the added ability to deal with both kernel and user pages. A completely non-blocking interface would be great, but that's a bit of work I'd rather not have to wait for. Maybe that requirement can be added later. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
