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block: queue data commands from the flush state machine at the head 

We used to insert the data commands following a pre-flush to the head
of the queue until commit 1e82fadfc6 ("blk-mq: do not do head insertions
post-pre-flush commands").  Not doing this seems to cause hangs of
such commands on NFS workloads when exported from file systems with
SATA SSDs.  I have no idea why this would starve these workloads,
but doing a semantic revert of this patch (which looks quite different
due to various other changes) fixes the hangs.

Fixes: 1e82fadfc6 ("blk-mq: do not do head insertions post-pre-flush commands")
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20230714143014.11879-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2023-07-14 16:30:14 +02:00 committed by Jens Axboe
parent 90b4622954
commit 9f87fc4d72
1 changed files with 1 additions and 1 deletions
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2
block/blk-flush.c
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@ -189,7 +189,7 @@ static void blk_flush_complete_seq(struct request *rq,
case REQ_FSEQ_DATA:
list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
spin_lock(&q->requeue_lock);
list_add_tail(&rq->queuelist, &q->flush_list);
list_add(&rq->queuelist, &q->requeue_list);
spin_unlock(&q->requeue_lock);
blk_mq_kick_requeue_list(q);
break;