On 2/2/20 12:14 AM, Andres Freund wrote: > Hi, > > On 2020-02-01 09:22:45 -0700, Jens Axboe wrote: >> On 2/1/20 2:43 AM, Andres Freund wrote: >>> Seems like either WILLNEED would have to always be deferred, or >>> force_page_cache_readahead, __do_page_cache_readahead would etc need to >>> be wired up to know not to block. Including returning EAGAIN, despite >>> force_page_cache_readahead and generic_readahead() intentially ignoring >>> return values / errors. >>> >>> I guess it's also possible to just add a separate precheck that looks >>> whether there's any IO needing to be done for the range. That could >>> potentially also be used to make DONTNEED nonblocking in case everything >>> is clean already, which seems like it could be nice. But that seems >>> weird modularity wise. >> >> Good point, we can block on the read-ahead. Which is counter intuitive, >> but true. > >> I'll queue up the below for now, better safe than sorry. >> >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index fb5c5b3e23f4..1464e4c9b04c 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -2728,8 +2728,7 @@ static int io_fadvise(struct io_kiocb *req, struct io_kiocb **nxt, >> struct io_fadvise *fa = &req->fadvise; >> int ret; >> >> - /* DONTNEED may block, others _should_ not */ >> - if (fa->advice == POSIX_FADV_DONTNEED && force_nonblock) >> + if (force_nonblock) >> return -EAGAIN; >> >> ret = vfs_fadvise(req->file, fa->offset, fa->len, fa->advice); > > Hm, that seems a bit broad. It seems fairly safe to leave > POSIX_FADV_{NORMAL,RANDOM,SEQUENTIAL} as sync. I guess there's there's > the argument that that's not something one does frequently enough to > care, but it's not hard to imagine wanting to change to RANDOM for a few > reads and then back to NORMAL. Yeah agree, not sure why I didn't cater to the normal cases. I'll adjust. -- Jens Axboe