On Fri, Aug 27, 2021 at 03:35:06PM -0700, Linus Torvalds wrote: > On Fri, Aug 27, 2021 at 2:32 PM Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > > > No, because you totally ignored the second question: > > > > If the directio operation succeeds even partially and the PARTIAL flag > > is set, won't that push the iov iter ahead by however many bytes > > completed? > > > > We already finished the IO for the first page, so the second attempt > > should pick up where it left off, i.e. the second page. > > Darrick, I think you're missing the point. > > It's the *return*value* that is the issue, not the iovec. > > The iovec is updated as you say. But the return value from the async > part is - without Andreas' patch - only the async part of it. > > With Andreas' patch, the async part will now return the full return > value, including the part that was done synchronously. > > And the return value is returned from that async part, which somehow > thus needs to know what predated it. Aha, that was the missing piece, thank you. I'd forgotten that iomap_dio_complete_work calls iocb->ki_complete with the return value of iomap_dio_complete, which means that the iomap_dio has to know if there was a previous transfer that stopped short so that the caller could do more work and resubmit. > Could that pre-existing part perhaps be saved somewhere else? Very > possibly. That 'struct iomap_dio' addition is kind of ugly. So maybe > what Andreas did could be done differently. There's probably a more elegant way for the ->ki_complete functions to figure out how much got transferred, but that's sufficiently ugly and invasive so as not to be suitable for a bug fix. > But I think you guys are arguing past each other. Yes, definitely. --D > > Linus
