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

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Message-ID: <A85FDAC1-5A0C-4F09-AB6D-B08A388A918B@cnexlabs.com>
Date:   Fri, 5 Jan 2018 19:56:31 +0000
From:   Javier Gonzalez <javier@...xlabs.com>
To:     Matias Bjørling <m@...rling.me>
CC:     Randy Dunlap <rdunlap@...radead.org>, 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 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.

Javier

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