On 11/4/2021 12:00 PM, Dan Williams wrote: >> >> If this understanding is in the right direction, then I'd like to >> propose below changes to >> dax_direct_access(), dax_copy_to/from_iter(), pmem_copy_to/from_iter() >> and the dm layer copy_to/from_iter, dax_iomap_iter(). >> >> 1. dax_iomap_iter() rely on dax_direct_access() to decide whether there >> is likely media error: if the API without DAX_F_RECOVERY returns >> -EIO, then switch to recovery-read/write code. In recovery code, >> supply DAX_F_RECOVERY to dax_direct_access() in order to obtain >> 'kaddr', and then call dax_copy_to/from_iter() with DAX_F_RECOVERY. > > I like it. It allows for an atomic write+clear implementation on > capable platforms and coordinates with potentially unmapped pages. The > best of both worlds from the dax_clear_poison() proposal and my "take > a fault and do a slow-path copy". > >> 2. the _copy_to/from_iter implementation would be largely the same >> as in my recent patch, but some changes in Christoph's >> 'dax-devirtualize' maybe kept, such as DAX_F_VIRTUAL, obviously >> virtual devices don't have the ability to clear poison, so no need >> to complicate them. And this also means that not every endpoint >> dax device has to provide dax_op.copy_to/from_iter, they may use the >> default. > > Did I miss this series or are you talking about this one? > https://lore.kernel.org/all/20211018044054.1779424-1-hch@xxxxxx/ I was referring to http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dax-devirtualize that has not come out yet, I said early on that I'll rebase on it, but looks like we still need pmem_copy_to/from_iter(), so. > >> I'm not sure about nova and others, if they use different 'write' other >> than via iomap, does that mean there will be need for a new set of >> dax_op for their read/write? > > No, they're out-of-tree they'll adjust to the same interface that xfs > and ext4 are using when/if they go upstream. > >> the 3-in-1 binding would always be >> required though. Maybe that'll be an ongoing discussion? > > Yeah, let's cross that bridge when we come to it. > >> Comments? Suggestions? > > It sounds great to me! > Thanks! I'll send out an updated patchset when it's ready. -jane
