On 2/9/21 12:55 PM, Andrew Morton wrote: > 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. Right, I think that'll be a round two on top of this, so we can make the write side happier too. That's a bit more involved... > 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! It's inherently racy, just like it is now. There's really no difference there, and I don't think there's a way to close that. Even if you modified filemap_write_and_wait_range() to be non-block friendly, there's nothing stopping anyone from adding dirty page cache right after that call. -- Jens Axboe
