From: NeilBrown <neilb@suse.com>
Date: Wed, 30 Aug 2017 13:47:12 +0200
Subject: [PATCH] drbd: remove BIOSET_NEED_RESCUER flag from
drbd_{md_,}io_bio_set
Git-commit: 974c58566e0b047d785701b6cf788a810072a4c1
Patch-mainline: v4.14-rc1
References: bsc#1104967,FATE#325924
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 <neilb@suse.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
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 92ba4c08835c..8cb3791898ae 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2178,13 +2178,12 @@ 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;
--
2.16.4