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@xxxxxx> Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- This patch needed to be refreshed after previous patch had long lines wrapped. Also added Ming's Reviewed-by. Thanks, NeilBrown 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 bc66cd595bef..3797753f4085 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -730,8 +730,7 @@ 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; -- 2.12.2
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