On Tue, Feb 9, 2021 at 10:25 PM Jens Axboe <axboe@xxxxxxxxx> wrote: > > 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, do you have some numbers before and after your patchset is applied? And kindly a test "profile" for FIO :-)? Thanks. - Sedat -
