From 93b27e72904a9869e648c870bf0d04b124fda1c7 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Sun, 18 Jun 2017 14:38:57 +1000 Subject: [PATCH] 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 Reviewed-by: Ming Lei Signed-off-by: NeilBrown Signed-off-by: Jens Axboe --- block/blk-core.c | 3 +-- 1 file changed, 1 insertion(+), 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; -- 2.20.1