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From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <keith.busch@intel.com>, Jens Axboe <axboe@kernel.dk>,
	Hannes Reinecke <hare@suse.de>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	linux-nvme@lists.infradead.org, linux-block@vger.kernel.org
Subject: Re: [PATCH 3/5] nvme: track shared namespaces
Date: Thu, 9 Nov 2017 18:09:48 +0200	[thread overview]
Message-ID: <1e0afeee-81d4-ca8e-4caa-2321640873e2@grimberg.me> (raw)
In-Reply-To: <20171109132046.GA22728@lst.de>


>>>>> To allow lockless path lookup the list of nvme_ns structures per
>>>>> nvme_ns_head is protected by SRCU, which requires freeing the nvme_ns
>>>>> structure through call_srcu.
>>>>
>>>> Can you remind me why isn't rcu sufficient? Can looking up a
>>>> path (ns from head->list) block?
>>>
>>> blk_mq_make_request can block.
>>
>> Oh I see, so can you explain why srcu should cover direct_make_request?
>>
>> What if we were to do:
>> --
>> 	rcu_read_lock();
>> 	ns = nvme_find_path(head);
>> 	rcu_read_unlock();
>> 	if (likely(ns)) {
>> 		...
>> --
> 
> That way we'd have to take and release a namespace reference for every I/O.

Yea,

I'm good,

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

WARNING: multiple messages have this Message-ID (diff)
From: sagi@grimberg.me (Sagi Grimberg)
Subject: [PATCH 3/5] nvme: track shared namespaces
Date: Thu, 9 Nov 2017 18:09:48 +0200	[thread overview]
Message-ID: <1e0afeee-81d4-ca8e-4caa-2321640873e2@grimberg.me> (raw)
In-Reply-To: <20171109132046.GA22728@lst.de>


>>>>> To allow lockless path lookup the list of nvme_ns structures per
>>>>> nvme_ns_head is protected by SRCU, which requires freeing the nvme_ns
>>>>> structure through call_srcu.
>>>>
>>>> Can you remind me why isn't rcu sufficient? Can looking up a
>>>> path (ns from head->list) block?
>>>
>>> blk_mq_make_request can block.
>>
>> Oh I see, so can you explain why srcu should cover direct_make_request?
>>
>> What if we were to do:
>> --
>> 	rcu_read_lock();
>> 	ns = nvme_find_path(head);
>> 	rcu_read_unlock();
>> 	if (likely(ns)) {
>> 		...
>> --
> 
> That way we'd have to take and release a namespace reference for every I/O.

Yea,

I'm good,

Reviewed-by: Sagi Grimberg <sagi at grimberg.me>

  reply	other threads:[~2017-11-09 16:09 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-02 18:30 nvme multipath support V6 Christoph Hellwig
2017-11-02 18:30 ` Christoph Hellwig
2017-11-02 18:30 ` [PATCH 1/5] nvme: track subsystems Christoph Hellwig
2017-11-02 18:30   ` Christoph Hellwig
2017-11-09 11:33   ` Sagi Grimberg
2017-11-09 11:33     ` Sagi Grimberg
2017-11-09 12:53     ` Christoph Hellwig
2017-11-09 12:53       ` Christoph Hellwig
2017-11-09 13:01       ` Sagi Grimberg
2017-11-09 13:01         ` Sagi Grimberg
2017-11-02 18:30 ` [PATCH 2/5] nvme: introduce a nvme_ns_ids structure Christoph Hellwig
2017-11-02 18:30   ` Christoph Hellwig
2017-11-02 18:30 ` [PATCH 3/5] nvme: track shared namespaces Christoph Hellwig
2017-11-02 18:30   ` Christoph Hellwig
2017-11-09 11:37   ` Sagi Grimberg
2017-11-09 11:37     ` Sagi Grimberg
2017-11-09 12:52     ` Christoph Hellwig
2017-11-09 12:52       ` Christoph Hellwig
2017-11-09 12:59       ` Sagi Grimberg
2017-11-09 12:59         ` Sagi Grimberg
2017-11-09 13:20         ` Christoph Hellwig
2017-11-09 13:20           ` Christoph Hellwig
2017-11-09 16:09           ` Sagi Grimberg [this message]
2017-11-09 16:09             ` Sagi Grimberg
2017-11-02 18:30 ` [PATCH 4/5] nvme: implement multipath access to nvme subsystems Christoph Hellwig
2017-11-02 18:30   ` Christoph Hellwig
2017-11-06 17:03   ` Mike Snitzer
2017-11-06 17:03     ` Mike Snitzer
2017-11-08  8:54   ` Christoph Hellwig
2017-11-08  8:54     ` Christoph Hellwig
2017-11-08 11:18     ` Hannes Reinecke
2017-11-08 11:18       ` Hannes Reinecke
2017-11-09  9:13       ` Christoph Hellwig
2017-11-09  9:13         ` Christoph Hellwig
2017-11-09 15:44   ` Hannes Reinecke
2017-11-09 15:44     ` Hannes Reinecke
2017-11-09 15:51     ` Christoph Hellwig
2017-11-09 15:51       ` Christoph Hellwig
2017-11-02 18:30 ` [PATCH 5/5] nvme: also expose the namespace identification sysfs files for mpath nodes Christoph Hellwig
2017-11-02 18:30   ` Christoph Hellwig

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