dm mpath: remove harmful bio-based optimization (dbaf971c) · Commits · 戴 / test

Removes the branching for edge-case where no SCSI device handler exists. The __map_bio_fast() method was far too limited, by only selecting a new pathgroup or path IFF there was a path failure, fix this be eliminating it in favor of __map_bio(). __map_bio()'s extra SCSI device handler specific MPATHF_PG_INIT_REQUIRED test is not in the fast path anyway. This change restores full path selector functionality for bio-based configurations that don't haave a SCSI device handler. But it should be noted that the path selectors do have an impact on performance for certain networks that are extremely fast (and don't require frequent switching). Fixes: ("dm mpath: remove unnecessary NVMe branching in favor of scsi_dh checks") Cc: stable@vger.kernel.org Reported-by:

Drew Hastings <dhastings@crucialwebhost.com> Suggested-by:

Martin Wilck <mwilck@suse.de> Signed-off-by:

Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

+1 −36

Original line number	Diff line number	Diff line
		@@ -599,45 +599,10 @@ static struct pgpath __map_bio(struct multipath m, struct bio *bio)
		return pgpath;
		}

		static struct pgpath __map_bio_fast(struct multipath m, struct bio *bio)
		{
		struct pgpath *pgpath;
		unsigned long flags;

		/* Do we need to select a new pgpath? */
		/*
		* FIXME: currently only switching path if no path (due to failure, etc)
		* - which negates the point of using a path selector
		*/
		pgpath = READ_ONCE(m->current_pgpath);
		if (!pgpath)
		pgpath = choose_pgpath(m, bio->bi_iter.bi_size);

		if (!pgpath) {
		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
		/* Queue for the daemon to resubmit */
		spin_lock_irqsave(&m->lock, flags);
		bio_list_add(&m->queued_bios, bio);
		spin_unlock_irqrestore(&m->lock, flags);
		queue_work(kmultipathd, &m->process_queued_bios);

		return ERR_PTR(-EAGAIN);
		}
		return NULL;
		}

		return pgpath;
		}

		static int __multipath_map_bio(struct multipath m, struct bio bio,
		struct dm_mpath_io *mpio)
		{
		struct pgpath *pgpath;

		if (!m->hw_handler_name)
		pgpath = __map_bio_fast(m, bio);
		else
		pgpath = __map_bio(m, bio);
		struct pgpath *pgpath = __map_bio(m, bio);

		if (IS_ERR(pgpath))
		return DM_MAPIO_SUBMITTED;

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