Re: [PATCH 2/2] nvme-multipath: do not fall back to __nvme_find_path() for non-optimized paths

[Christoph Hellwig <hch@lst.de>]

On Tue, Jul 28, 2020 at 08:25:18AM +0200, Hannes Reinecke wrote:
>> Maybe instead of the early return put the following condition on else?
>
> That depends on whether we want to have a fallback to __nvme_find_path() or 
> not. With your suggestion we would lose that; I'd rather keep it.

Why would we want to fall back?  nvme_round_robin_path only
returns NULL in case there is a single disabled path, in which
case __nvme_find_path won't find anything either.  I'd go for something
like this:

---
From 4f578364a3d15898c7d715315a3371b2f71db416 Mon Sep 17 00:00:00 2001
From: Hannes Reinecke <hare@suse.de>
Date: Mon, 27 Jul 2020 18:08:03 +0200
Subject: nvme-multipath: do not fall back to __nvme_find_path() for
 non-optimized paths

When nvme_round_robin_path() finds a valid namespace we should be using it;
falling back to __nvme_find_path() for non-optimized paths will cause the
result from nvme_round_robin_path() to be ignored for non-optimized paths.

Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/multipath.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 93c70e1591de8f..3ded54d2c9c6ad 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -281,10 +281,13 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
 	struct nvme_ns *ns;
 
 	ns = srcu_dereference(head->current_path[node], &head->srcu);
-	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR && ns)
-		ns = nvme_round_robin_path(head, node, ns);
-	if (unlikely(!ns || !nvme_path_is_optimized(ns)))
-		ns = __nvme_find_path(head, node);
+	if (unlikely(!ns))
+		return __nvme_find_path(head, node);
+
+	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
+		return nvme_round_robin_path(head, node, ns);
+	if (unlikely(!nvme_path_is_optimized(ns)))
+		return __nvme_find_path(head, node);
 	return ns;
 }
 
-- 
2.27.0


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