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authorNeilBrown <neilb@suse.com>2017-06-18 06:38:57 +0200
committerJens Axboe <axboe@kernel.dk>2017-06-18 20:40:59 +0200
commit93b27e72904a9869e648c870bf0d04b124fda1c7 (patch)
tree93c444acadcdd8e0b7f62b1fa6f545c776fb1a3a /block
parentblk: make the bioset rescue_workqueue optional. (diff)
downloadlinux-93b27e72904a9869e648c870bf0d04b124fda1c7.tar.xz
linux-93b27e72904a9869e648c870bf0d04b124fda1c7.zip
blk: use non-rescuing bioset for q->bio_split.
A rescuing bioset is only useful if there might be bios from that same bioset on the bio_list_on_stack queue at a time when bio_alloc_bioset() is called. This never applies to q->bio_split. Allocations from q->bio_split are only ever made from blk_queue_split() which is only ever called early in each of various make_request_fn()s. The original bio (call this A) is then passed to generic_make_request() and is placed on the bio_list_on_stack queue, and the bio that was allocated from q->bio_split (B) is processed. The processing of this may cause other bios to be passed to generic_make_request() or may even cause the bio B itself to be passed, possible after some prefix has been split off (using some other bioset). generic_make_request() now guarantees that all of these bios (B and dependants) will be fully processed before the tail of the original bio A gets handled. None of these early bios can possible trigger an allocation from the original q->bio_split as they are either too small to require splitting or (more likely) are destined for a different queue. The next time that the original q->bio_split might be used by this thread is when A is processed again, as it might still be too big to handle directly. By this time there cannot be any other bios allocated from q->bio_split in the generic_make_request() queue. So no rescuing will ever be needed. Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-core.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 9bd10c46a538..62cf92550512 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -790,8 +790,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
if (q->id < 0)
goto fail_q;
- q->bio_split = bioset_create(BIO_POOL_SIZE, 0, (BIOSET_NEED_BVECS |
- BIOSET_NEED_RESCUER));
+ q->bio_split = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
if (!q->bio_split)
goto fail_id;