linux-kernel - Re: [PATCH] lightnvm: fix memory leak when submit fails

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Message-ID: <59a735f0-9fef-5e6d-f7eb-851e14a2883e@lightnvm.io>
Date:   Thu, 21 Jan 2021 19:25:37 +0100
From:   Matias Bjørling <mb@...htnvm.io>
To:     Heiner Litz <hlitz@...c.edu>
Cc:     Jens Axboe <axboe@...nel.dk>, Pan Bian <bianpan2016@....com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lightnvm: fix memory leak when submit fails

On 21/01/2021 17.58, Heiner Litz wrote:
> I don't think that ZNS supersedes OCSSD. OCSSDs provide much more
> flexibility and device control and remain valuable for academia. For
> us, PBLK is the most accurate "SSD Emulator" out there that, as
> another benefit, enables real-time performance measurements.
> That being said, I understand that this may not be a good enough
> reason to keep it around, but I wouldn't mind if it stayed for another
> while.

The key difference between ZNS SSDs, and OCSSDs is that wear-leveling is 
done on the SSD, whereas it is on the host with OCSSD.

While that is interesting in itself, the bulk of the research that is 
based upon OCSSD, is to control which dies are accessed. As that is 
already compatible with NVMe Endurance Groups/NVM Sets, there is really 
no reason to keep OCSSD around to have that flexibility.

If we take it out of the kernel, it would still be maintained in the 
github repository and available for researchers. Given the few changes 
that have happened over the past year, it should be relatively easy to 
rebase for each kernel release for quite a while.

Best, Matias



>
> On Thu, Jan 21, 2021 at 5:57 AM Matias Bjørling <mb@...htnvm.io> wrote:
>> On 21/01/2021 13.47, Jens Axboe wrote:
>>> On 1/21/21 12:22 AM, Pan Bian wrote:
>>>> The allocated page is not released if error occurs in
>>>> nvm_submit_io_sync_raw(). __free_page() is moved ealier to avoid
>>>> possible memory leak issue.
>>> Applied, thanks.
>>>
>>> General question for Matias - is lightnvm maintained anymore at all, or
>>> should we remove it? The project seems dead from my pov, and I don't
>>> even remember anyone even reviewing fixes from other people.
>>>
>> Hi Jens,
>>
>> ZNS has superseded OCSSD/lightnvm. As a result, the hardware and
>> software development around OCSSD have also moved on to ZNS. To my
>> knowledge, there is not anyone implementing OCSSD1.2/2.0 commercially at
>> this point, and what has been deployed in production does not utilize
>> the Linux kernel stack.
>>
>> I do not mind continuing to keep an eye on it, but on the other hand, it
>> has served its purpose. It enabled the "Open-Channel SSD architectures"
>> of the world to take hold in the market and thereby gained enough
>> momentum to be standardized in NVMe as ZNS.
>>
>> Would you like me to send a PR to remove lightnvm immediately, or should
>> we mark it as deprecated for a while before pulling it?
>>
>> Best, Matias
>>
>>