On Thu, Jun 17, 2021 at 09:23:51AM +0100, David Howells wrote: > > Here are some patches to fix netfs_write_begin() and the handling of THPs in > that and afs_write_begin/end() in the following ways: > > (1) Use offset_in_thp() rather than manually calculating the offset into > the page. > > (2) In the future, the len parameter may extend beyond the page allocated. > This is because the page allocation is deferred to write_begin() and > that gets to decide what size of THP to allocate. > > (3) In netfs_write_begin(), extract the decision about whether to skip a > page out to its own helper and have that clear around the region to be > written, but not clear that region. This requires the filesystem to > patch it up afterwards if the hole doesn't get completely filled. > > (4) Due to (3), afs_write_end() now needs to handle short data write into > the page by generic_perform_write(). I've adopted an analogous > approach to ceph of just returning 0 in this case and letting the > caller go round again. Series looks sane. I'd like to hear about the thp-related plans in more detail, but that's a separate story. > I wonder if generic_perform_write() should pass in a flag indicating > whether this is the first attempt or a second attempt at this, and on the > second attempt we just completely prefill the page and just let the partial > write stand - which we have to do if the page was already uptodate when we > started. Not really - we'll simply get a shorter chunk next time around (with the patches in -next right now it'll be "the amount we'd actually managed to copy this time around" in case ->write_begin() tells us to take a hike), and that shorter chunk is what ->write_begin() will see. No need for the flags...
