Careful analysis shows that this flag is not needed. The RESCUER flag is only needed when a make_request_fn might: - allocate a bio from the bioset - submit it with generic_make_request() or similar - allocate another bio from the bioset
The second allocation can block until the first bio is processed, so a rescuer is needed to ensure the first bio does get processed. With a rescuer it will only get processed when the make_request_fn completes. In drbd, allocations from drbd_io_bio_set happen from drbd_new_req() or w_restart_disk_io() which is only called to handle RESTART_FROZEN_DISK_IO. In former is called precisely once from the make_request_fn. The later is never called by within the make_request_fn. So there cannot be two allocations in the same call to the make_request_fn, so a rescuer is not needed. Allocations from drbd_md_io_bio_set are used for IO to the bitmap and the activity log. There are only accessed from worker threads and workqueues, never directly from make_request_fn. Again, the rescuer isn't needed. Signed-off-by: NeilBrown <[email protected]> --- drivers/block/drbd/drbd_main.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c index e2ed28d45ce1..4fe7c058a573 100644 --- a/drivers/block/drbd/drbd_main.c +++ b/drivers/block/drbd/drbd_main.c @@ -2167,13 +2167,12 @@ static int drbd_create_mempools(void) goto Enomem; /* mempools */ - drbd_io_bio_set = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_RESCUER); + drbd_io_bio_set = bioset_create(BIO_POOL_SIZE, 0, 0); if (drbd_io_bio_set == NULL) goto Enomem; drbd_md_io_bio_set = bioset_create(DRBD_MIN_POOL_PAGES, 0, - BIOSET_NEED_BVECS | - BIOSET_NEED_RESCUER); + BIOSET_NEED_BVECS); if (drbd_md_io_bio_set == NULL) goto Enomem; -- 2.14.0.rc0.dirty
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