On Mon, 8 Feb 2021 19:30:05 -0700 Jens Axboe <axboe@xxxxxxxxx> wrote: > Hi, > > For v1, see: > > https://lore.kernel.org/linux-fsdevel/20210208221829.17247-1-axboe@xxxxxxxxx/ > > tldr; don't -EAGAIN IOCB_NOWAIT dio reads just because we have page cache > entries for the given range. This causes unnecessary work from the callers > side, when the IO could have been issued totally fine without blocking on > writeback when there is none. > Seems a good idea. Obviously we'll do more work in the case where some writeback needs doing, but we'll be doing synchronous writeout in that case anyway so who cares. Please remind me what prevents pages from becoming dirty during or immediately after the filemap_range_needs_writeback() check? Perhaps filemap_range_needs_writeback() could have a comment explaining what it is that keeps its return value true after it has returned it!
