On Thu, Oct 21, 2021 at 08:00:50PM +0200, Andreas Gruenbacher wrote: > On Thu, Oct 21, 2021 at 7:09 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > This discussion started with the btrfs search_ioctl() where, even if > > some bytes were written in copy_to_sk(), it always restarts from an > > earlier position, reattempting to write the same bytes. Since > > copy_to_sk() doesn't guarantee forward progress even if some bytes are > > writable, Linus' suggestion was for fault_in_writable() to probe the > > whole range. I consider this overkill since btrfs is the only one that > > needs probing every 16 bytes. The other cases like the new > > fault_in_safe_writeable() can be fixed by probing the first byte only > > followed by gup. > > Hmm. Direct I/O request sizes are multiples of the underlying device > block size, so we'll also get stuck there if fault-in won't give us a > full block. This is getting pretty ugly. So scratch that idea; let's > stick with probing the whole range. Ah, I wasn't aware of this. I got lost in the call trees but I noticed __iomap_dio_rw() does an iov_iter_revert() only if direction is READ. Is this the case for writes as well? -- Catalin
