linux-kernel - Re: [PATCH] nvme: lightnvm: expose OC devices as zero size to OS

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Message-ID: <b6ad4793-11a5-2958-f01e-b62774541299@lightnvm.io>
Date:   Mon, 25 Mar 2019 11:56:36 +0100
From:   Matias Bjørling <mb@...htnvm.io>
To:     Marcin Dziegielewski <marcin.dziegielewski@...el.com>
Cc:     igor.j.konopko@...el.com, Keith Busch <keith.busch@...el.com>,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: lightnvm: expose OC devices as zero size to OS

On 3/18/19 2:32 PM, Marcin Dziegielewski wrote:
> On 3/14/19 2:56 PM, Matias Bjørling wrote:
>> On 3/14/19 6:41 AM, Marcin Dziegielewski wrote:
>>> Open channel devices are not able to handle traditional
>>> IO requests addressed by LBA, so following current
>>> approach to exposing special nvme devices as zero size
>>> (e.g. with namespace formatted to use metadata) also
>>> open channel devices should be exposed as zero size
>>> to OS.
>>>
>>> Signed-off-by: Marcin Dziegielewski <marcin.dziegielewski@...el.com>
>>> ---
>>>   drivers/nvme/host/core.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>>> index 07bf2bf..52cd5c8 100644
>>> --- a/drivers/nvme/host/core.c
>>> +++ b/drivers/nvme/host/core.c
>>> @@ -1606,7 +1606,8 @@ static void nvme_update_disk_info(struct 
>>> gendisk *disk,
>>>       if (ns->ms && !ns->ext &&
>>>           (ns->ctrl->ops->flags & NVME_F_METADATA_SUPPORTED))
>>>           nvme_init_integrity(disk, ns->ms, ns->pi_type);
>>> -    if (ns->ms && !nvme_ns_has_pi(ns) && !blk_get_integrity(disk))
>>> +    if ((ns->ms && !nvme_ns_has_pi(ns) && !blk_get_integrity(disk)) ||
>>> +        ns->ndev)
>>>           capacity = 0;
>>>       set_capacity(disk, capacity);
>>>
>>
>> Marcin,
>>
>> The read/write as traditional I/Os feature is supported in OCSSD 2.0. 
>> For example, one can hook support up through the zone device support 
>> in the kernel. There is a patch here that enables it here:
>>
>> https://github.com/OpenChannelSSD/linux/commit/e79e747601a315784e505d51a9265e82a3e7613c 
>>
>>
>> With that, an OCSSD device can be used as a traditional zoned block 
>> device, and use the existing infrastructure. Which is really neat.
>>
>> It is not upstream, since it depends on some features that we 
>> introduce with zoned namespaces, but in general, tools can read/write 
>> from a block device as any other, just honoring the special write 
>> rules that are for OCSSD/zoned block devices.
>>
>> -Matias
> 
> Matias,
> 
> If zone related changes will be in upstream soon, I agree that this 
> patch is not needed.
> 
> But, I can not agree that tools can use OCSSD device as normal block 
> device - for example in current implementation I don't see way to send 
> erase request and of course without it we can not send write. Because of 
> that, it was my intention to block normal IO to OCSSD device by default.
> 
> Marcin

It is implemented the same way as "Zone reset" is implemented in 
ZAC/ZBC. The kernel converts the trim to a vector erase and issues that 
instead.