linux-kernel - Re: [GIT PULL 18/25] lightnvm: set target over-provision on create ioctl

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Date:   Fri, 5 Jan 2018 12:17:23 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Javier Gonzalez <javier@...xlabs.com>,
        Matias Bjørling <m@...rling.me>
Cc:     Jens Axboe <axboe@...com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hans Holmberg (C)" <hans.holmberg@...xlabs.com>
Subject: Re: [GIT PULL 18/25] lightnvm: set target over-provision on create
 ioctl

On 01/05/2018 11:56 AM, Javier Gonzalez wrote:
>> On 5 Jan 2018, at 20.53, Matias Bjørling <m@...rling.me> wrote:
>>
>> On 01/05/2018 08:52 PM, Javier Gonzalez wrote:
>>>> On 5 Jan 2018, at 20.33, Randy Dunlap <rdunlap@...radead.org> wrote:
>>>>
>>>> On 01/05/2018 05:16 AM, Matias Bjørling wrote:
>>>>> From: Javier González <javier@...xlabs.com>
>>>>>
>>>>> Allow to set the over-provision percentage on target creation. In case
>>>>> that the value is not provided, fall back to the default value set by
>>>>> the target.
>>>>>
>>>>> In pblk, set the default OP to 11% of the total size of the device
>>>>
>>>>> +#define PBLK_DEFAULT_OP (11)
>>>>
>>>> Hi,
>>>> Just curious -- where does 11 come from?  Is it a spec value?
>>> 11 stands for 11% over-provisioning for the media to allow garbage
>>> collection. Different SSDs have different values based on the targeted
>>> workload - 11% is a common default value for standard drives.
>>> The spec. does not specify any default values of over-provisioning.
>>> Javier.
>>
>> I think what Randy means is, why is the value not 20% or 7%, which is the traditional over-provisioning on SSDs.
> 
> We decided 11% based on customer input, but 7% and 20% are also good
> default values. I'm ok with having any of those as default - anyone
> caring about OP will define the value on target creation, which is the
> primary objective of this patch.

Got it.  Thanks.

-- 
~Randy