On Mon, Oct 16, 2023 at 08:48:27AM -0700, Darrick J. Wong wrote: > Hmm. xfs_prepare_ioend converts unwritten cowfork extents to written > prior to submit_bio. So I guess you'd have to trick writeback into > issuing totally separate bios for the single mapping. Yes. Hitting IOEND_BATCH_SIZE seems like the least difficult one to hit, but even that would require work. > Then you'd have > to delay the bio for the higher offset part of the mapping while > allowing the bio for the lower part to complete, at which point it would > convey the entire mapping to the data fork. Shouldn't really matter which side is faster. > Then you'd have to convince > the kernel to reread the contents from disk. I think that would be hard > since the folios for the incomplete writeback are still uptodate and > marked for writeback. directio will block trying to flush and > invalidate the cache, and buffered io will read the pagecache. I don't think on a live kernel it is possible. But if one of the two bios completed before the other one, and power failed just inbetween.
