Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > This can't be used with content encryption as that may require expansion of > > the write RPC beyond the write being made. > > > > This doesn't affect writes via mmap - those are written back in the normal > > way; similarly failed writethrough writes are marked dirty and left to > > writeback to retry. Another option would be to simply invalidate them, but > > the contents can be simultaneously accessed by read() and through mmap. > > > > I do wish Linux were less of a mess in this regard. Different > filesystems behave differently when writeback fails. Cifs is particularly, um, entertaining in this regard as it allows the write to fail on the server due to a checksum failure if the source data changes during the write and then just retries it later. > That said, the modern consensus with local filesystems is to just leave > the pages clean when buffered writeback fails, but set a writeback error > on the inode. That at least keeps dirty pages from stacking up in the > cache. In the case of something like a netfs, we usually invalidate the > inode and the pages -- netfs's usually have to spontaneously deal with > that anyway, so we might as well. > > Marking the pages dirty here should mean that they'll effectively get a > second try at writeback, which is a change in behavior from most > filesystems. I'm not sure it's a bad one, but writeback can take a long > time if you have a laggy network. I'm not sure what the best thing to do is. If everything is doing O_DSYNC/writethrough I/O on an inode and there is no mmap, then invalidating the pages is probably not a bad way to deal with failure here. > When a write has already failed once, why do you think it'll succeed on > a second attempt (and probably with page-aligned I/O, I guess)? See above with cifs. I wonder if the pages being written to should be made RO and page_mkwrite() forced to lock against DSYNC writethrough. > Another question: when the writeback is (re)attempted, will it end up > just doing page-aligned I/O, or is the byte range still going to be > limited to the written range? At the moment, it then happens exactly as it would if it wasn't doing writethrough - so it will write partial folios if it's doing a streaming write and will do full folios otherwise. > The more I consider it, I think it might be a lot simpler to just "fail > fast" here rather than remarking the write dirty. You may be right - but, again, mmap:-/ David
