On Mon, Jan 22, 2018 at 11:35:49AM +0800, Ming Lei wrote: > DM-MPATH need to allocate request from underlying queue, but when the > allocation fails, there is no way to make underlying queue's RESTART > to restart DM's queue. > > This patch introduces blk_get_request_notify() for this purpose, and > caller need to pass 'wait_queue_entry_t' to this function, and make > sure it is initialized well, so after the current allocation fails, > DM will get notified when there is request available from underlying > queue. > > This approach is suggested by Jens, and has been used in blk-mq dispatch > patch for a while, see blk_mq_mark_tag_wait(). > > Suggested-by: Jens Axboe <[email protected]> > Cc: Mike Snitzer <[email protected]> > Cc: Laurence Oberman <[email protected]> > Cc: Bart Van Assche <[email protected]> > Signed-off-by: Ming Lei <[email protected]> > --- > block/blk-mq-tag.c | 27 ++++++++++++++++++++++++++- > block/blk-mq.c | 24 +++++++++++++++++++++--- > block/blk-mq.h | 1 + > include/linux/blk-mq.h | 5 +++++ > 4 files changed, 53 insertions(+), 4 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 336dde07b230..911fc9bd1bab 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -128,10 +128,35 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data > *data) > if (tag != -1) > goto found_tag; > > - if (data->flags & BLK_MQ_REQ_NOWAIT) > + if ((data->flags & BLK_MQ_REQ_NOWAIT) && !(data->notifier && > + (data->flags & BLK_MQ_REQ_ALLOC_NOTIFY))) > return BLK_MQ_TAG_FAIL; > > ws = bt_wait_ptr(bt, data->hctx); > + > + /* > + * If caller requires notification when tag is available, add > + * wait entry of 'data->notifier' to the wait queue. > + */ > + if (data->flags & BLK_MQ_REQ_NOWAIT) { > + bool added = false; > + > + spin_lock_irq(&ws->wait.lock); > + if (list_empty(&data->notifier->entry)) > + __add_wait_queue(&ws->wait, data->notifier); > + else > + added = true; > + spin_unlock_irq(&ws->wait.lock);
The above need a per-notifier lock too, since the same notifier may be added to different wait queues at the same time. -- Ming
