On Mon, Nov 22, 2021 at 09:48:35AM +0200, Sagi Grimberg wrote:

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+	bool			alloc_srcu;

I found the following statement multiple times in this patch:

WARN_ON_ONCE(q->alloc_srcu != !!(q->tag_set->flags & BLK_MQ_F_BLOCKING));

Does this mean that the new q->alloc_srcu member variable can be left out
and that it can be replaced with the following test?

q->tag_set->flags & BLK_MQ_F_BLOCKING

q->tag_set can't be used anymore after blk_cleanup_queue() returns,
and we need the flag for freeing request_queue instance.

Why not just look at the queue->srcu pointer? it is allocated only
for BLK_MQ_F_BLOCKING no?

Yeah, we can add one extra srcu pointer to request queue, but this way
needs one extra fetch to q->srcu in fast path compared with current
code base, so io_uring workload may be affected a bit.

Thanks,
Ming