On Wed, Oct 25, 2023 at 03:34:40PM -0400, Mike Snitzer wrote:
> From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> Update DM core's IO submission to allocate required memory using
> GFP_NOWAIT if REQ_NOWAIT is set. Lone exception is in the error path
> where DM's requeue support needs to allocate a clone bio in
> dm_io_rewind() to allow the IO to be resubmitted: GFP_NOWAIT is used
> first but if it fails GFP_NOIO is used as a last resort.
>
> Tested with simple test provided in commit a9ce385344f916 ("dm: don't
> attempt to queue IO under RCU protection") that was enhanced to check
> error codes. Also tested using fio's pvsync2 with nowait=1.
>
> But testing with induced GFP_NOWAIT allocation failures wasn't
> performed.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Co-developed-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> drivers/md/dm-io-rewind.c | 13 ++++++--
> drivers/md/dm.c | 66 ++++++++++++++++++++++++++++++++-------
> 2 files changed, 65 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/md/dm-io-rewind.c b/drivers/md/dm-io-rewind.c
> index 6155b0117c9d..bde5a53e2d88 100644
> --- a/drivers/md/dm-io-rewind.c
> +++ b/drivers/md/dm-io-rewind.c
> @@ -143,8 +143,17 @@ static void dm_bio_rewind(struct bio *bio, unsigned int bytes)
> void dm_io_rewind(struct dm_io *io, struct bio_set *bs)
> {
> struct bio *orig = io->orig_bio;
> - struct bio *new_orig = bio_alloc_clone(orig->bi_bdev, orig,
> - GFP_NOIO, bs);
> + struct bio *new_orig;
> +
> + new_orig = bio_alloc_clone(orig->bi_bdev, orig, GFP_NOWAIT, bs);
> + if (unlikely(!new_orig)) {
> + /*
> + * Returning early and failing rewind isn't an option, even
> + * if orig has REQ_NOWAIT set, so retry alloc with GFP_NOIO.
> + */
> + new_orig = bio_alloc_clone(orig->bi_bdev, orig, GFP_NOIO, bs);
> + }
dm_bio_rewind() is only called in requeue work fn, so there shouldn't
be issue with NOWAIT, cause upper IO submission code path won't be blocked
by requeue.
Thanks,
Ming
