From: Javier Gonzalez <javier@cnexlabs.com>
To: =?utf-8?B?TWF0aWFzIEJqw7hybGluZw==?= <m@bjorling.me>
CC: Randy Dunlap <rdunlap@infradead.org>, Jens Axboe <axboe@fb.com>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Hans Holmberg (C)" <hans.holmberg@cnexlabs.com>
Subject: Re: [GIT PULL 18/25] lightnvm: set target over-provision on create
 ioctl
Thread-Topic: [GIT PULL 18/25] lightnvm: set target over-provision on create
 ioctl
Thread-Index: AQHThid5Ni7fXf6Z1ESl/E9DppO7pqNlq+mAgAAFJwCAAAB0gIAAALkA
Date: Fri, 5 Jan 2018 19:56:31 +0000
Message-ID: <A85FDAC1-5A0C-4F09-AB6D-B08A388A918B@cnexlabs.com>
References: <20180105131621.20808-1-m@bjorling.me>
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 <05ea1992-8dae-f961-b2e0-a93727edc2b5@bjorling.me>
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> On 5 Jan 2018, at 20.53, Matias Bj=C3=B8rling <m@bjorling.me> wrote:
>=20
> On 01/05/2018 08:52 PM, Javier Gonzalez wrote:
>>> On 5 Jan 2018, at 20.33, Randy Dunlap <rdunlap@infradead.org> wrote:
>>>=20
>>> On 01/05/2018 05:16 AM, Matias Bj=C3=B8rling wrote:
>>>> From: Javier Gonz=C3=A1lez <javier@cnexlabs.com>
>>>>=20
>>>> 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.
>>>>=20
>>>> In pblk, set the default OP to 11% of the total size of the device
>>>=20
>>>> +#define PBLK_DEFAULT_OP (11)
>>>=20
>>> 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.
>=20
> 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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